I'm a girl, so I'm not filling out the vote... but oh my gosh. It can vary widely.
The first time I squirted was totally unexpected---it was just a guy friend (we'd been lovers the past summer, but were platonic during the summer in question, until he asked if I wanted to come over so he could practice some technique.) I guess he probably knew what he was doing (it was just manual stimulation, a few fingers inside me) but when I squirted, he was totally shocked and ran off to the bathroom for towels. I was shocked and embarrassed---I knew what squirting was obviously, but I was like "oh my gosh, he just ran away, maybe he doesn't know it's not pee?" So sheepishly tried to explain to him, he sheepishly answered that he knew already... he was totally an "everything in its place, nothing dirty" sort of person, excellent with design and programming of course, but you could tell it really upset him to have his bed be wet. So we cleaned up and went to the kitchen and made dinner, awkwardly talked about small things, and I walked home.
The next time we hung out (platonically again, obviously) we just never mentioned it.
So, I felt all uneasy and was like "wow, I hope that never happens again."
Except that I tried to get myself to do it so I could figure it out... no success.
My current partner, I was kind of shocked again that he got me to squirt just from PIV sex a week or two after we started sleeping together---but in the afterglow I was like "so that was new," and he was like "yeah, it's cool, I get tactile proof that I'm good to you." I asked if it was usual and he said a good amount of his past partners had squirted, so a) his cock is perfect and b) he wasn't surprised or taken aback.
I've gone on to learn a lot about my body and its responses now, so if I ever was to shack up with a new partner I'd ask how they felt about squirting somewhere in the lead-up to sex, and if they were uncomfortable or uneducated I'd either decide not to have sex, or I'd just focus on him and keep my own panties on. I don't really want a repeat of that first time...