i have been doing this for a while now, its kinda fun to just screw off with it.
but heres what you do...
get on a horde blood DK and go to Stormwind tram then
get in a little bit of pvp combat, use rune tap then run through the tram entrance. once u get to the other side, your rune tap CD will reset.
if u want u can just keep hoping through it and keep spaming rune tap.
this sort of works for some other abilities too but its not garanteed. for example i noticed that anti-magic shell will sometimes reset but not always.
you can do this for as long as you want with 10 allies trying to kill you and u basicly have unlimted health
this may work for other classes too but i dont know