Bottoms Up

This achievement can be accomplished anywhere by imbibing any algohol during combat and then downing mobs. If each character carries 3-4 alcohol (Ithbank is common) then it can be imbibed in combat after mobs have been weakened and before they die.

The easiest all-at-once method might be in Act 2. Near the area where you met the Harpers, you will find an old building and a clickable "Raven" along side the road. If you click the raven you are suddenly in combat and get attacked by many birds. I used one Ithbank (any alcohol will do).. gave the drink to Gale and waited until the ravens encircled the party, then cast shatter on them all. No more angry birds. Achievement complete.