Take a shot every 10 seconds whenever you hear a Sexophone, the Leitmotif of the Magypsies. This includes the different-yet similar version used by a reconstructed New Fassad, who is actually Locria, the last, missing Magypsy.
Take a two shots whenever someone mentions manliness. Mainly occurs with Flint in Chapter 1, but it's also used as a big Funny Moment for Lucas in Chapter 8.
Take a shot whenever you hear any version of King P's theme, such snippets that accompany several Pigmask cutscenes.
Drink a whole glass when you hear the last major version of the theme, the one that plays when you fight King Porky himself.
Take a shot every time the Masked Man attacks with lightning. Whether it's in a cutscene or during a fight with him, take a shot for each target he hits his lightning with.
Allow the party to drown and go back to the beginning, however, and you'll have to down the shot you were holding AND the take another shot right after. Going underwater again starts the entire process over again. Have fun!
Take a shot for every character-, and object-based hallucination you run into on Tanetane Island. There are plenty.
In particular, take three shots if you went into the beautiful hot spring during the hallucination, Only to discover that said beautiful hot spring was actually a REALLY filthy sludge pond.
If you allow the Ultimate Chimera to touch and kill your party during Chapter 7 and the bathroom dungeon in Chapter 8, take three big shots.