Correct, of course. And it was the Cat.
- is Casey from Sports Night
and
- is Steve from Family Matters
#?) I hate broccoli and yet, in a certain sense, I am broccoli
Stewie, Family Guy
I’m fairly certain he doesn’t say that, but even if he does, it’s not what I was thinking. But right type of show.
Bingo!
I’ll repost in with numerics. 
- “You know, we’re not the only ones destroying trees. What about beavers? You call yourself an environmentalist, why don’t you go club a few beavers?”
Sir Humphrey, Yes Minister.
Corporal Agarn in multiple episodes of F Troop.
That may be the only episode of Buffy I’ve ever watched. Couldn’t name the guy that said it.
24: “I have a new girlfriend for you, son. Her name is Barbie and she lives in Malibu. She already has a boyfriend named Ken, but he’s not much of a man… I checked.”
The Critic - Jay’s Father.
It must be Clerks : The Animated Series. Dante, to Randall. Repeated gag.
Bingo…
I pretty much had to go with the repeated gag, otherwise a quote from a show with a broadcast run of two episodes may have been a bit obscure.
You’re kidding, right? 
I used “Crumbs, crumbs, crumbs, yay!” just the other day in casual conversation… and there was a time when I couldn’t go a week without saying “Who is driving? Oh my god, Bear is driving, how can that be?”
It’s Xander. And darn you!
“I’m a rich kid with issues. Lots of issues.”
“Try to save everyone and all you’ll end up with is a lot of enemies and a messiah complex.”
“I’m not a eunuch!”
If CandidGamera’s are 25, 26, and 27, then I got 28 next:
-
“I’m Jack Valenti, and these are my cheeks!”
-
“If I had a dollar for every brain you didn’t have, I’d have one dollar.”
Freakazoid!
WAG: Milly from This Life?
Ted Knight, The Mary Tyler Moore Show, Eulogy for Chuckles the Clown
No. (Although, like the Sports Night quote, I supposed it’s possible that someone else wrote the same line of dialog for another show.)
Xander Harris from Buffy the Vampire Slayer and Sir Humphrey Appleby from Yes, Minister are correct. Is anybody going to take a shot at #18?