A Sennen - A Sennen is when someone sticks their fingers up your butt,

A Sennen is when someone sticks their fingers up your butt, and it's so popular from a dumb anime where a guy used it to beat up another guy.

My cousin did a Sennen on me at my birthday. It was the worst thing ever.

My teacher did a Sennen on the class. I got a detention and a laugh.

My brother did a Sennen on my dog. The dog cried.