Baramutsu!!

Mutsumi shows up to ruin Hara’s ideal fishing trip day and tops it off by destroying his brand new $1,000 fishing reel. Hara then sets out an elaborate plot to pretend to be fishing buddies with the guy, develop a deep friendship, and then get the ultimate revenge... by catching the oilfish! This “fatty tuna” has so much oil that the human body can’t digest it all and disposes of the excess oil through one's butt. This slippery fish is going to help make it so that Mutsumi never shows his face around a fishing pole ever again!

(Source: Manga Planet)