The end of "Stan's Old Owner" when Stan realizes his old owner was more of an evil scientist than he let on. Stan tell him to come close so he can whisper to him the secret of how he can talk. Then, once he is within Stan's reach, Stan gives him a stiff jab.
Another one from the same episode, Stan gives a brief bio on a new character and here's what he says about Ian:
Stan: Dr. Ian Calloway, AHHHHHHH!
In "Too Short", when the kids are at school Stan makes sculptures of them out of cheese to keep him company, then eats them questioning why he made them out of cheese.
From "Freaky Fido"
Stan: I'm gonna need an agent, sunglasses, and a political cause I don't really understand.
Tyler's attempt to walk down the stairs to get to Bennett's play while wearing a full-body cast in "The Green-Eyed Monster". Had this troper crying from laughter.
In one episode, Stan was complaining he didn't get any leftovers, and then he said that he would get revenge by "photobombing all the family pictures". Cue intro, in which, he does just that (as he does for every intro).
In "Who's Training Who?", the entire eponymous exchange between the dog trainer (played by Leigh Allyn Baker and Stan. At first they start Kung-Fu Fighting (yes, a dog Kung-Fu Fighting) only for it to be revealed as a daydream sequence - which actually makes it even funnier as the dog trainer begs and cries for Stan to get off the couch (and she's been at it for an hour!)