Arkham Asylum:

You sneak into a finger-painting session. Gain 1 Sanity.

You suddenly realize that all the paint is brown...

Lose 1 lunch.

Close but the best encounter is actually at the bank.

"Stand behind an old lady counting pennies. Lose 1 Sanity"

lol I agree, the finger painting one caused my crew to laugh for about 30 mins straight when it came up. Something about the late hour and the way my friend read the card just made everyone bust a gut laughing.

Spilling a bottle of ink and losing a sanity from looking at the random pattern it formed.

2nd place: Carless picknickers unleashing monsters

Must've been one hell of an anthill...