Positional Chubby

Getting an often unwanted erection simply because of the way you're sitting or positioned. Too much blood flowing to the wrong place and always at the wrong time.

"I was sleeping when the teacher called me to the front of the class. When I woke up I was pitching a pretty big tent and there was no way I could hide it."

"Sounds to me like you got a positional chubby...God I hate those."