I think this line from SNL when Teri Hatcher dressed up as David Spade and vice versa:
David Spade: Oh, yeah? Well, you know, I did a movie called "Black Sheep." Maybe you saw it the first time, when it was called "Tommy Boy"!
The bit where they impersonate F/As is classic:
Richard Hayden: Ok, folks, the guy in front of you is Tommy, he's gonna be taking you through my little spiel here. Tommy is a Scorpio, he likes biking and he's never been laid. Okay... seatbelts. Just put the little thing into the big thing and... I tell ya what. If you don't know how to fasten your seatbelt, just raise your hand and I'll have Tommy Boy here come back there and hit you in the head with a tack hammer because you're a RETARD. And, the life vests, these you might need. But what are the chances of us hitting a lake. If my money says anything, it's gonna be a mountain.