Towards the end when there is a TV report about a ghost attack at the Thanksgiving Day Parade. The TV has been knocked on it's side and is shown as such. There is a quick cut to the team watching it with there heads turn sideways to see it. Why is it funny? Because you the player most likely have your head turned the same way as them.
You and the other guys have defeated the Juvenile Slor and escaped the crumbling Shandor Island within seconds of its total collapse. Ray starts excitedly asking about what you just defeated, only to be glared at by the rest of the team - especially Egon.
Egon: SHUT UP.
When the elevator at the Sedgewick temporarily stops-
PETER: "Think we're stuck", well let's see... *leans towards panel, presses a few buttons* Think we're stuck, think we're stuck, think we're stuck... Ray, uh, you guys okay with officially stuck in the elevators? Show of hands?
* Rookie raises his hand*
*Peter, Ray, and Rookie get ready for Slimer. Cut to the elevator doors.*
PETER: Kill it, Ray!
*Egon opens the elevator doors.*
EGON: Need a hand?
PETER: You always fail me, don't you?
Arguably the funniest thing about this scene? Egon is strong enough to pry apart stuck elevator doors with his bare hands!
One of the Cursed Artifacts you find is a pair of bellbottom pants. Description: These pants keep on truckin' - WITH NOTHING IN THEM. Extra points for disco music when you pick them up. It gets even better when you make it back to the firehouse and find that the pants are not put away somewhere like the other artifacts; they follow you around.
ANSWERING MACHINE: Dr. Spengler, this is James from We Ship It. Listen, you gotta come down and pick up this package of Carpathian Dunnbach[?] mold we've been holding for you. It's started to spread, it's taken over half the loading docks, and I (pause) I think it's singing?!
Ray speculating on what the other mood slimes react to:
I wonder what their purpose is, what they would react to? Happiness, sadness, anger, sunlight, moonlight, orbital convergence, shooting stars, prayer, screaming, candles, spotlights, diet or regular... the possibilities are endless!
One of Janine's many phone conversations:
Janine: Ghostbusters. *pause* No, we do not recommend you attempt to perform a level 5 Peruvian exorcism on yourself. *pause* But after you've tied yourself up, it would be incredibly difficult to do that to the cat, even if you could catch it.
Vigo's painting has many funny things to say. A complete list can be found here, under the section "Vigo Insults".
"I should have had a bathroom painted in this thing."
"Pull my finger. I command you."
"I dreamt I was in a painting with ponies. It was nice."
"I see the evil of the times to come. You will remember paying $1.45 for gas and will weep hot tears for yesterday."
"I see the evil of the times to come. No flying cars - ever! HAHAhahahaha!"
"I see the evil of the times to come. The glove won't fit."
After you defeat the Stay Puft Marshmallow Man, the answering machine at the office gives us this little gem:
"I was wondering if it's safe to eat all this marshmallow goo that's fallen over Times Square. And as a followup question, what if I already did?"
Another one from Janine:
Janine: Hello, Ghostbusters. No, we do not summon the ghosts of dead relatives and then capture them so you can ask them the combination to the safe. Same to you, pal.
Ray and Peter discussing the restraining order that the maid from the first movie had put on them - just in time to rack up another.
Peter chastising the Rookie for accidentally falling over the side of the building - leading into the Stay Puft boss battle - saying his insurance hasn't been paid up yet.
Peter: Hey, Ray? Say three guys, the size of your finger, knocked you off a 30-story building and you had to climb alllll the way back up to tear 'em apart... how mad mad would you be at those three little... dinky types?
After the library level, there's a message left for Ray on the answering machine. He owes approximately 418 dollars in late fees. Gets funnier when you adjust it for inflation. That 418 bucks in 1991? Over $730 in 2014 dollars!