I was going to write a post about the greatest tanka ever, but then I discovered that someone had already beaten me to it. IZAAAK!!!

I will go ahead and post the Japanese original, just because I can:

廻文
ある人の放屁しけるをかたへの人わらふあまりに廻文の歌よめといひければ
へゝゝゝゝへゝゝゝゝゝゝへゝゝゝゝへゝゝゝゝゝゝへゝゝゝゝゝゝ

The poet was Kabocha no Motonari (加保茶元成), and you can find this poem collected in the 徳和歌後万載集 (Tokuwakagomanzaishuu).