When they're in desperate need of $80,000 fast ... and Alan, the losingest loser of the lot, puts on his suit, sits down at the blackjack table, and in a single montage takes the casino for the entire sum. The random numbers and formulae that appear adds the Mundane Made Awesome value too.
Stuart chewing out Melissa at the end after suffering her abuse for the entire film (and throughout their relationship).
A similar predicament to Stu chewing out Melissa in the first movie, with Stu's future father-in-law treating him like crap the whole time, he then gives the father-in-law a good "World of Cardboard" Speech about how he (Stu) has a demon inside him and that while, yes, he lost Teddy in Bangkok, he and his friends managed to get Teddy back. It ends up giving the father-in-law a newfound respect for Stu.
The opening scene. It starts with an horrified Thai prison warden, flanked by two guards in riot gear, running into a chaotic Prison Riot. The warden nonchalantly shoves his way straight through the middle of the riot and makes his way to the Chow's prison cell in the back. Then, ignoring the chaos around him, the warden pulls the poster in Chow's cell away from the wall and discovers Chow's escape hole.
Stu chasing Chow in Vegas in the limo. Preceded by:
Stu: I'm just a dentist!
Phil: No. You're a fucking doctor. Now go get him.
Chow killing Marshal and his goon from behind and saving the Wolfpack.