Tap the brakes lightly so he/she will have to respond. They should get the idea soon enough, This works in the car as well, a small tap to bring the brake lights on and people soon drop back..
I can't believe this kind of attitude. How stupid to risk your own safety by trying to show up the idiot behind who's riding or driving too close. You're the bigger idiot.
And the moron (or troll?) who deliberately got rear ended and ended up hurt as a result! Doh, how clever are you?
Do it in a car especially and you are very likely to end up with no compo and facing 'without due care' charges. Contrary to popular belief you are at fault if hit from behind if you've caused it.