I'm the bottom you'd be doing it to. The only reason I would ask for a pull out, is that I want his load in my mouth or I have some other use for his cum.
But what ever my reasoning is, I would communicate that prior to him fucking me. If he fails at the pull out, he can just feed it to me from his cock or fingers.
Now with that said, If a bottom wants a pull out so he's able to collect the load for another use, it's the Top's jizz until someone receives it, so the bottom should let him know the plan. If the bottom wants the pull out to avoid infections, well, there's too many words to describe a guy like that. But here's a few: he's lazy, he's greedy, always points the finger at someone else, wont be held accountable for what he does, selfish, did I say lazy? If I was the top and knew this was the reason for the pull out request, I'd flip him on his belly, lean down on his face down head with one hand and pin his arm behind his back with the other hand. Then pump his ass full, as deep as i can get it. Then shrug my shoulders and say oops.