A back and forth battle utilizing Facebook's poking mechanism. Person A pokes person B. Person B then pokes back. And then the original poker pokes back the poke backer who then pokes back...etc etc. This is known as a poke war. Poke wars accomplish nothing, except of course when one participant finally gives in therefore relinquishing their soul and any dignity that is attached to it.
Note: Poke wars can also be a semi-pathetic attempt at actually having human contact or just flirting in general without having to worry about following up in any way.
Friend 1: did you hear about Monica's and Huw's poke war on Facebook?
Friend 2: Yeah! Monica totally won that shit!
After 3 solid months of poking back and forth Cate finally relented and subjected herself to the ultimate humiliation of a poke war defeat.
Also a great usage, is to show how Ann is that bit more better then Melly and overall totally put him in his place.
Warning: If you can't get the better of a person in real life(specifically brothers) you should not attempt to do so through Poke Wars...it will only lead to inevitable defeat...felix!