I guess I'm not the spontaneous sort. I usually set up encounters with plenty of lead time, disclose my HIV status upfront and my desire to take the load. And...I have a few friends with benefits. I remember the first time I barebacked years after learning I was HIV positive. We'd set it up, I'd told him the score. When he was about to fuck me (as in I was in position and he was about to enter), he asked "Do you want to take the load?" I answered "This is an option? SURE!!!!!!!!" From then on out, I just made it clear I wanted it bare. If people don't want to that, no hard feelings, I just move on.
The moral of this story is, never run after a bus, a train, a cab or a man. There's always another one coming along.