Monk: I’m going to use my feat “throw anything” to deliver a coup de grace on the goblin by throwing the other goblin at it!
Cue the rest of the party giggling like mad
DM: You can only coup de grace with a melee weapon.
Monk: Aw, come on, a goblin isn’t a melee weapon?!
DM: Well in this case it’s a ranged weapon.