Something outstandingly funny (to the extent that the reader could wet himself), sometimes written абассака or обоссака. Comes from обоссаться (to wet oneself).
Ха-ха-ха, такая обассака: Пермь — сибирский аэропорт. Чета кремлевские пропагандисты из пушки мимо воробья промазали.
Ha-ha-ha, what a joke: Perm is a Siberian airport. Seems the propaganda guys from the Kremlin to have tried and failed to use a sledgehammer to crack nuts.
(ivanytch @ ЖЖ, 07/2009)