I rarely go at it without Porn. So there's never much of a chance to 'fill in' with mental imagery. I do use mental imagery to get myself in the mood. When that happens most of the time I reach for triggers. Sometimes a trigger loses its punch if I go there too often. When that happens I try to float new triggers to see if they work as well.
An alpha male twice my size power fucking me up against a wall or barrier.
Imaging friends I'd like to have sex with having sex and I'm a voyeur.
Straight alpha males overwhelming women with their seductive male power.
Sex tease in a locker room, half way out of sweaty gym gear.
Jason Branch watching his partner Brad having sex with other men. In particular him watching Brad have sex with Colton Ford, whom he left Jason for.
Str8 men bringing women to multiple orgasms.
Rimming. More rimming. Marathon rimming.
This list seems to suggest the str8 scenarios happen frequently, which isn't the case. And when they do somehow the women are never as fleshed out in my imagination as the guy.
One thing I have noticed, it is RARE that I can think back on a porn flick, any porn flick and get excited about reliving it in my mind. Watch it? I'm busting big time. But thinking about it, not so much. I don't know why that is.
On the other hand I can think about personal experiences and love on them big time. But they aren't sufficient to get off to. I'd rather imagine the other guy in a new scenario. Which brings me to the most important part of my mental imagery: I'm not in it.