My party was invading a Necromancer's tower, and he eventually throws some zombies at us.

The party Ranger throws two alchemist fire at them, dealing about 8 damage to them (we were low-level). Another round goes by and they take a little more damag,e but are still alive...

Then the player remembers somethin...
Ranger: Wait! I forgot Undead are my Favored Enemy!
DM: Uh.. Does this affect the damage from alchemist fire?
Ranger: I dunno... It'd be cool though...

Since our DMing filosophy is "If we are not sure how a rule works, rule it in the way it benefits the players the most.", the DM agreed with the extra damage.

Ranger... okay, so that's extra 4 damage to each zombie.
DM: They are destroyed. You burned them WITH HATE!!!
*group laughs*

A little while later, he tries to Bluff a Vampire into believing we were soldiers, but fails the check by 1. Then he remember he gets a +2 bonus on Bluff checks against favored enemies. Surprisingly, it's enought to pass the check against the Vampire's Sense Motive.

DM: You convince him... WITH HATE!
Druid: Hah... And they say love makes the world go round!
*group laughs again*

I suppose it was a lot funnier at the time ^^
Still funny to me! From now on, that's how rangers work in my head.