Its Walky/WMG

Joe Rosenthal's extraordinary gift with women is actually an Abductee power.
He (and probably the rest of Squad 48, his original team) is part of an experiment to make Abductees who are irresistible to the opposite sex and completely insatiable sexually, to ensure that the Martian genes spread through the human gene pool, creating a Master Race of perfect soldiers.
 * However, in the prequel comic Roomies!, Joe is implied as being just as successful with the ladies - BEFORE his abduction! Unless he has been abducted before, this could mean his abilities represent a non-alien mutation. Alternatively, his existing power over the ladies was amplified by his abduction. Also notably, his luck seems to not be so hot with other abductees - this could indicate that every other abductee has the power of resisting his gift (though why this would be isn't so clear).
 * It's well-established in the later IW strips that "abduction" is an ongoing process that starts in early childhood, if not earlier.
 * It's to discourage inbreeding in such a small population. The abductees are less attracted to each other to encourage them to spread their genetic material amongst the general population instead.

Mike is a beer-powered soul generator.
He's normally what could be described as a soulless monster, but he end up not only normal, but a polite, outgoing person with only a few sips of beer. After he vomits, he goes back to his normal self, despite the alcohol that should remain in his bloodstream. The Mike in Shortpacked! may be an effect of testing this to reanimate someone still alive by getting Mike extremely drunk and cloning them in his presence. No use other than making backup Mikes has yet been found, and nobody wants a backup mike (aside from the writer and fans). He only shows up in purgatory because the universe looked at his soul-defused mind, said "close enough," and chucked him in there.

Mike has telepathic powers.
He uses telepathy to figure out your weak point which he later (or immediately) exploits. Alcohol inhibits his powers, which is why he's much nicer when he's drunk.

Mike was really happy as a child.
He grew up with a loving family and had an overall very happy childhood. He was later abducted by aliens, which he was okay with, because aliens are pretty awesome. However, the breaking point in Mike's mentality was when he discovered that the aliens had given him powers... but didn't give him the power to choke people with his mind.

The aliens killed Peppermint Patty.
The shock of this caused the then-teenage Marcie to lose her voice and develop her slightly warped sexuality. Only the shock of Joe turning down sex caused her to overcome the psychological barrier on her voice, and only failing to stop the violent deaths of three squadmates and casual lovers brought her back to a position where she could return to meaningful relationships with Jason.