With a Capital T

...and that stands for "Trope."

This is when a character emphasises the magnitude of the thing they're talking about by saying that it's a Thing "with a capital T". They may go on to add that the capital letter also stands for something else relevant.

Can be played for laughs by having the character get the initial letter wrong (or deliberately changing it to make a point), or announcing that the entire first syllable is capital.

Examples of With a Capital T include:

Advertising

An Australian public safety ad (about germ awareness) from the 1970s used a version of "Ya Got Trouble" from The Music Man:

Oh, you got trouble!
With a capital "T"
And that rhymes with "D"
And that stands for dirt!

Fan Works

After an instance of With a Capital T in the Mega Crossover story My Apartment Manager is not an Isekai Character (specifically "Moving Days, Part I"), the narrator goes on to add a Shout-Out to The Music Man:

Over the next couple days we got Busy with a capital "B". (Which rhymes with "D", which stands for "Deadline"...)

Film

In a scene in 100 Girls, the protagonist imagines the hypothetical trials he would be prepared to put up with for his dream girl, which include a mother-in-law who is "a big witch with a capital B".
- The gag here being, of course, that the "B" goes on the second word.
  - Of course, it's got a trope named after it, so everyone can probably guess anyway.
Back to The Future Part II:

Biff: Hello? Hello? Anybody home? Huh? Think, McFly! Think! Your old man, Mr. Loser?
Marty: What?
Biff: That's right. Loser with a capital "L".

Brain Donors:

Roland: And that spells cash with a capital...
Jacques: K!
Roland: You should go back to school.
Jacques: I hated teaching.

Peter's Friends:

Andrew: It's shit with a capital "sh".

Stuck on You:

Cher: I was a bitch with a capital C.

Live-Action TV

Red Dwarf, episode "Waiting for God":

Cat: I'm smooth, with a capital Smoo.

From an episode of As the World Turns:

Henry Coleman: These are dangerous people, with a capital D, which means death, which could happen to you.

Psych, episode "Rob-a-Bye Baby":

Shawn Spencer: Dude, this blows, with a capital Z.

Roseanne, episode "Vegas, Vegas":

Roseanne: Marriage stinks, with a capital SUCK!

Veronica Mars, episode "Look Who's Stalking":

Kendall: Oh, well if it isn't Little Miss Teen Getaway. Your dad and I were just dealing with a little trouble.
Veronica: Like, trouble with a capital "T", that rhymes with "C", that stands for...
Keith: Veronica!
Veronica: What? I was going to say "cute."

In the Will and Grace episode "Coffe & Commitment", Jack meets a guy who describes as "cute with a capital Q".
On Glee, Kurt has been called "capital G gay."

Music

"My Resistance is Low":

I'm going Overboard with a capital O

"Eadie Was A Lady":

Eadie had class with a capital K.

Theatre

The Trope Namer is "Ya Got Trouble" from The Music Man:

Oh, we got trouble!
Right here in River City!
With a capital "T"
And that rhymes with "P"
And that stands for pool!

Video Games

In the second Discworld game, Ridcully uses the term "Glitter, with a capital 'gluh'!"
Kingdom Hearts II:

Axel: You really don't remember. It's me? You know, Axel?
Roxas: Axel?
Axel: Talk about blank with a capital B.

Strong Bad's Cool Game for Attractive People, episode 4:

Coach Z: Strong Bad, you kidding? You can't put Senor Cardgage in your movie! That guy is creepy with a capital "cree"!

In MadWorld, the Black Baron considers one of the minigames he introduces as "Easy with a capital EZ".

Western Animation

Ed, Edd 'n' Eddy has "trouble with a capital 'R'".
From an episode of Baby Blues:

Bizzy: That guy's a loser with a capital 'Loo'.

Beast Wars, episode "The Agenda", referring to a situation involving the villainous Blackarachnia:

Rattrap: We've got trouble! Oh yeah, trouble... with a capital "B"!

- Also, in "Tangled Web", concerning approaching Maximals:

Quickstrike: We got trouble brewing outside. Trouble with a capital "M"!

From an episode of GetBackers:

Kazuki Fuchouin: He's hazardously lucky, isn't he?
Kakei Juubei: With a capital... hazardous.

From an episode of G.I. Joe:

Ace: Uh-oh. What we got here is a game of dirty pool. With a capital "D" for Destro!

Happy Feet:

Ramon: We got personality, with a capital Y. Why? Because we're hot!

Rugrats Go Wild:

Spike: Will you stop worrying? I know all about cats with a capital "K".

The Tick, episode "Evil Sits Down For a Moment":

The Tick: Falling in love with a supervillain is Trouble with a capital 'troub'.

Legion of Super Heroes, episode "Unnatural Alliances":

Duo Damsel: Terra-Man, word is you've been terrorizing this entire prairie in search of someone.
Star Boy: The only thing you're gonna find here is trouble.
Bouncing Boy: With a capital "L"!

Real Life

This is where the name of The Teetotaler comes from. In the 1840s or so, people were pledging themselves to "T-Total Abstinence" from alcohol.