Pretenemy is a portmanteau of "pretend" and "enemy."
Contrast with frenemy (friend and enemy), in which case there is definitely a genuine measure of emnity. Both frenemies and pretenemies, however, are friends on some level.
I'm pretty sure David and myself are pretenemies. We argue a lot but there is no real anger or disagreement, and we consider it entertaining. At least, I do...
Me: "I have an example in mind: 'But isn't Quinn just your pretenemy?'
"'No, he has no pretenemies. Everyone actually hates him.'"
David: "But you don't know Quinn has no pretenemies for a fact."
Me: "It doesn't matter, it's Urban Dictionary. It's an example."
David: "Then it's a dictionary, it has to be accurate."
Me: "This is why we're pretenemies."