When you think you are hidden behind an object but someone can clearly see the top of your head poking over it. The term is more widely used in video games where you are unaware of your players model and therefore have no idea your head is sticking out.
Jeremy: How did you know i was there, do you have wallhacks?
Ben: Nah mate, you were doing a Thundering Joel.
Jeremy: Damn it!
Ben: Nah mate, you were doing a Thundering Joel.
Jeremy: Damn it!
by The Doeh November 12, 2015