Cross-Cultural Handshake

If shaking hands isn't a culture-specific habit, it sure seems like it ought to be. So Science Fiction authors who are trying to be clever will come up with some other gesture for alien cultures to use for the same purpose.

The trouble is, shaking hands probably developed to its present form because it's a darned convenient thing for our human bodies to do. Obviously, other species have other ways of greeting each other, but the Media Watchdog would never let you show humanoids sniffing each other's genitalia. There are cultural differences in the way various groups go about the whole handshaking thing, but these are fairly subtle and the TV audience might not notice.

As a result, it seems like a lot of aliens shake hands by grasping each other's forearms, which is actually an old earth method of shaking hands, by showing that you have no weapons in your sleeves, as a display of trust.

Examples of Cross-Cultural Handshake include:

Film

In Demolition Man, handshaking has evolved into a curious formal wave due to an increasing aversion to physical contact. When Spartan greets a fellow officer by grabbing his hand, the officer is visibly shocked by the intimacy.

Literature

The Ickiest Handshake trophy surely belongs to the Sakuntala from Alan Dean Foster's Drowning World. These monkey-like aliens have extremely long tongues like an anteater's and respectfully greet each other by wrapping their tongues around one another's faces. Furthermore while they understand that humans aren't physically equipped to do that, most are offended if a human won't at least touch tongue-tips with them.
- An un-squicky variant from the same 'verse would be the Tran practice of breathing in each other's faces, to share precious warmth on their inhospitable ice world.
In The Conquerors Trilogy by Timothy Zahn, the aliens have poisonous tongues (which are also capable of being used as slicing weapons). They greet each other by cutting up a fruit with their tongues which neutralizes their poison. Damn intimidating the first time a human prisoner sees them do this. Worse, the human was expected to follow suit... or at least do his best.
In Snow Crash the customary greeting in the Metaverse is bowing, not shaking hands; the Metaverse is a visual-only virtual reality so actually touching another avatar is impossible.

Live-Action TV

In Andromeda
- Nietzscheans hold their forearms together to form a double-helix. Curiously, this leaves their other hand out of sight of the other guy, making it easy to pull a weapon. Given their survivalist nature, this makes perfect sense.
The Centauri in Babylon 5 do a double forearm-shake.
- Which like a lot of their culture, is similar to late Roman tradition. The Narn occasionally do a similar gesture though with just one hand; there is also their closed fists to chest gesture, which seems to be more formal.
  - Sometimes the Narns also roll their fists around each other before making that gesture though this mostly seems to occur during the first season; possibly it was deemed looking slightly silly.
Vulcans in Star Trek have their own distinctive salute which is used in lieu of a handshake. Some Fanon suggests that, as Vulcans are touch-telepaths, shaking hands would seem excessively intimate to them. While Star Trek Enterprise makes this interpretation unlikely, it has some support in the fact that a second form of greeting, involving the touching of the fingertips, is occasionally seen only between family members.
- A couple of other quick Star Trek examples: Cardassians have been shown to press their palms together to say goodbye to each other, but it only showed up a couple of times. Bajorans didn't have a weird handshake, but they did have a weird clap: they (and several other races, including the Wadi) applauded with the back of one hand to the other palm instead of palms together.
  - The Bajorans vedeks have a habit of randomly walking up to a Bajoran and grasp their left ear (the right ear is covered by an elaborate earring) to feel their pagh. In one EU novel, Ro Laren reveals that this is the reason she wears her earring on the left ear - she hates it when they do that.
  - Klingons have been seen to do it sometimes as well.
- Cardassians also had a weird clap; in one scene with Bajorans and Cardassians attending a speech by Gul Dukat, the Bajorans gave the clap mentioned above (as usual), while the Cardassians drummed their hands on the table.
  - Some human cultures do this too.
The Jaffa and Tok'ra of Stargate SG-1 both do the forearm shake.
Parodied in Red Dwarf; Kryten and the GELF leader present their hands as if to shake hands but instead reach past each other's hands and grab the other's ankles and then bounce up and down on their other legs.
Ultronians in My Hero shake elbows while reciting "Sneet snader sneet"...
...which is no less ridiculous than Mork's "Na-Nu Na-Nu" and hand gesture from Mork and Mindy

Newspaper Comics

Parodied in one Dilbert strip where Ratbert attempts to infiltrate a gang of elves who have been terrorizing Dilbert. They ask for the secret handshake and he performs a ridiculous pose with his arms waving and his head sticking out from between his legs. One elf replies that he's wrong but it's "one heckuva good guess".

Tabletop Games

In Paranoia, all secret society groups have handshakes or handshake equivalents. The fun part is that most of these handshakes start off in a very similar manner...

Web Original

Homestar Runner once showed Homestar and the King of Town demonstrate a secret handshake. Neither of them have arms.
- Later Strong Bad and The Cheat do it and theirs is similarly devoid of armic activity.

Western Animation

One Robot Chicken sketch involves members of the Alpha Psi fraternity meeting up and immediately performing their secret handshake which is very complicated and involves loads of bodily harm.
The Futurama episode "Mars University" had Bender discovering a chapter of his old robot fraternity and being asked to do the secret handshake to prove it. Said handshake involved both robots locking hands and then snaking their telescoping arms in ludicrous fashion, ending by spinning their wrists so fast it generates a miniature nova. And Bender accidentally takes one of the other guy's fingers in the process.
This happened in the last half of Interstella 5555.
The Plutarkian Traditional Greeting from Biker Mice From Mars: Stand facing away from each other and then bend over to present the buttocks. Rub your buttocks against those of your compatriot whilst chanting "cheek to cheek, and stink to stink, as Plutark rules, the galaxy shrinks!" and then shake the head rapidly from side to side whilst whooping before standing up and making three armpit-farts.
In Galaxy High, when Doyle and Aimee first met Milo de Venus, they didn't know which hands they're supposed to shake, as Milo has three arms on each side. Milo just told them to shake all hands.

Real Life

An Earth-based example: it's most common to shake hands with the right hand in Western culture. The Scout Association shakes with the left hand. This tradition originated with the Scouts in Africa where Baden-Powell observed tribesmen shaking with the left hand being a gesture of trust; the shield being carried in the left hand, you had to put your shield down, indicating your trust for the other guy, in order to greet him.
The Maori hongi, a greeting-gesture in which people touch noses, thus sharing the breath of life. Though if it's between women, it often turns into a mutual kiss on the cheek.