Why would two trolls in kismesis want to have troll frick frack? I thought they were supposed to hate each other to some extent and want to kill each other. How could you get them to get close enough together to do that or am I misunderstanding?

That’s not what a kismessitude is. It’s more like an arche-rivalry, where they’ll make fun of each other and maybe fight on occasion, but mostly just try to one up each other.  And they don’t out right hate each other, it’s more like they dislike one another but respect and admire them. 

Good examples of this can be found in a lot of anti-heros/edgy characters like Vegeta from Dragon Ball Z or Shadow from Sonic. Where they don’t generally like the hero but respect their drive and abilities and constantly want to out do them