The act of masturbating under your blankets. "Opening the Umbrella" refers to the similar movements and look of someone opening an umbrella.
1. Jim: Dude, I just caught Billy opening the umbrella in his bed!
2. Earl: Oh! What are you doing there?
Steve: Nothing. Just opening an umbrella under here.
2. Earl: Oh! What are you doing there?
Steve: Nothing. Just opening an umbrella under here.
by Ol' CB August 5, 2010
An expression that depicts a psychologically painful act as shoving an umbrella into your ass and open it inside. It's like kicking one's butt, but much more painful.
This job is really sucks, plus my boss hates me, I feel like he is going to open the umbrella inside.
by Gyrun March 19, 2018