Ai-in

Ai-in or ain (アイーン) (pronounced ah-EEN or AIEEN) is a Japanese pop culture word originated by comedian Ken Shimura (志村けん) for his bakatono (バカ殿) character (a fool/clown in white makeup and Japanese garb). Usually, it's said while making a slicing motion under the chin and grimacing. The word was further popularized by the popular all-girl quartet Minimoni (ミニモニ。), who features the character in two of their promotional videos ("Ai-in Dance no Uta" and "Ai-in Taisou").

What the word means has been a matter of debate. One source suggests it means, "Enough!", and the slicing gesture makes this a reasonable if not completely credible definition. Most seem to feel that ai-in is a nonsense word, used primarily for comic effect.