When a guy tells me he's going to come, or I feel those first contractions of his, I like to push down on him as hard as I can, getting every bit in, then, I bear down like I'm trying really hard to poop. This pushes my intestines closer to the entry, and forces his cock into my colon. I can feel that happen big time, like a firm resistance, or hitting the end of the tunnel, then, suddenly it goes thru. If you've never felt this, you will know when it happens, cause it feels like there's suddenly a LOT more cock in you. This usually starts my orgasm, and I can feel his contractions as he comes.
I can tell when he's come well into my colon, because usually the cum doesn't come back out. Sometimes it comes out an hour later. (a word of warning if you're at the supermarket when it comes out!)
Finishing inside my vagina is okay, but usually it's a 'finish-where-you-start' kind of thing. Since I don't prefer vaginal sex, it's not a thing that have to deal with too often.
Getting came on your face is a lot less exciting that pornography makes it out to be generally.
But to each his or her own! My girl's ultimate fantasy is having me pull out to cum on her face and tits, then shove my cock back in for a second cum deep in her ass. I only wish I could recover so quickly...