Reddit.
Al-redi-reddi-tt.
Ten. (Shame this one doesn't work too well for reddit - the funniest part of this joke is the third punchline enjoying people struggle to understand what the hell you're talking about.)
A mocking bird!
One's fun to hit with a sledge hammer, the other one's a water melon.
3. One to screw it in, the next to claim credit and the third to be a bot that reposts.