The scene in the first movie when Tangina and Diane argue about who should go into the Portal.
Tangina: You never done this before!!
Diane: Neither have you!!
Tangina: (beat) You're right, you go!!
When Steven tries to answer Tangina psychically, it seems like she didn't hear him, but...
Tangina: I just don't like trick answers.
The final shot of the movie, where the family enters a hotel room and then shoves the TV outside, is pretty comical.
In the first movie, when the family brings Dr. Lesh and her team in, Dr. Lesh's reaction to seeing the Poltergeists in the room is pretty hilarious. A jump cut of her sipping coffee/tea with her hands absolutely shaking.
One of her assistants talks about a previous case where he videotaped a matchbox car traveling across a room by itself, taking 7 hours to get from one side to another. Steve just goes "uh-huh" and opens the door to Carol-Anne's room and walks away, leaving Dr. Lesh and her assistants to stare at all of the stuff flying around the room.
Also, Dr. Lesh saying it'd be hard to determine whether the house is haunted..followed immediately by a coffee pot sliding across the table all by itself
And of course, there's the "remote duel" in the beginning.
The car being angry as a Running Gag. Apparently according to Taylor the car is sentient and only works when it wants to. As seen in the finale of 2.
Steven: You can stay in the house, you can have my aura, my spirit, the ghosts, the whole deal. The WHOLE CASABA!!!!! But keep your hands off my car. Hands off!!! It's worse than it was before.
Taylor: The car's still angry huh?
Steven: Angry? That car is PISSED!!!
The opening scene of the first film, in which the dog systematically goes through the entire house to munch on whatever snacks the family members had with them when they dozed off, can be amusing. It's like the dog's seen Dad fall asleep in front of the television so many times, it considers that the signal that it's safe to go chow down.