Some guys, getting a blowjob, squeeze their eyes shut and go "oh oh oh nnnggghhh ahhh yes." Some guys pretty much go "yep, you're blowing me alright, how bout that" in a totally unfazed tone of voice. Some guys start out unfazed but let out a few grunts just as they get up to their orgasm. And a surprising number of guys seem unfazed by their orgasms! I have a couple of male friends whose external reaction to coming amounts to not much more than "welp, there it goes."
This is particularly hard for me to understand because I'm way over at the other end of the spectrum, the one where a fingertip brushing against me sends me into the Screams Of The Damned. Sometimes I try to suss out how voluntary this is for me. (I've sometimes fantasized about a scene where I was strongly encouraged not to make a peep; I have no idea how successful I'd be at that.) I know I'm able to get the noise level down to relatively subdued pants and moans, but I don't know if I'm capable of keeping a totally level face and voice. I suspect I'm not. The sheer intensity of what I feel during sex is just too goddamn much for me to keep inside.
I've only seen one woman able to do the "welp, there it goes," and it was tremendously frustrating for me. I was plowing away at her with an enormous strap-on, and she was kinda just lying there like I was doing her nails, then gave out a single little "oh" like she was almost starting to feel something, but stopped. Afterwards she told me that I made her come. That was the "oh." Wow.
The funny thing is that the noise a guy makes seems utterly unconnected to how sexually enthusiastic he is. I have a friend who does the "yep, I just came, how bout that," and he's a horny bastard who absolutely loves to fuck and is famed for jerking off any time he's not fucking. So clearly he's feeling something intense internally. I always wonder if sex actually feels different to more reactive people or if only their reactions are different, but ultimately it's a "does the blue I see look like the blue you see?" problem--there's no way to know.
All I know is that when fucking makes me literally scream, it's not a form of attention-seeking or even deliberate self-expression; it's just one of many things my body does pretty much without me when it's getting fucked. I just can't feel "OH MY GOD OOOHHHHHH" without saying "OH MY GOD OOOOHHHHH," and I'm fascinated that anyone can.