This is tricky.
As someone who does have a clue, I often just shrug when I see folks do the most idiotic things, and...they do do some stupid ass stuff.
I've offered free advice a time or two and it's generally not well received. (Ignorant people are, after all, ignorant.)
I think the answer to your question is how it's framed what it's about, and if the person you see seems approachable.
I can't stand folks who won't do a little research for themselves. When it gets down to it...a muscle has a certain range of motion. It's really not that complicated. You can train for muscular, or sacroplasmic, hypertrophy; train to raise your AT or whatever. It's all well documented science.
I think, in most cases it's not a bad idea to train intuitively, and watch those who seem like they really know what they're doing.
All, that being said, if a person is seriously committed, I don't mind telling them they need to eat, or go home and recover (that's where the gains are made).
Personal trainers...the vast majority in franchised gyms...are often idiots...with no sound basis in experience, nor training other than being a glorified rep counter, and often are completely clueless. E.g., having a 50 year old overweight woman do NASM unbalanced exercises: stupid in the n'th degree. She needs to walk every night with her husband, for starters. Unbalanced exercise is the last thing she needs. Weight bearing exercise for her as she gets into motion.
Free advice: stay cool. It effects your exercise performance in a major way. If you see a moron in rubber sweats, a hat, or a ghetto outfit....believe the obvious: that person doesn't know how to approach training in the most effective way. DUMB.
The answer, I guess, is you have to be perceptive. We all have the same 24 hours in a day. If you see me circuit training, and I'm humming along, please, let me get my training done. That doesn't mean I'm not a giver, nor a nice guy. That means I need to execute my own plan for success which includes lifting, cardio, stretching, etc....and...I need to get it done before it's time to eat again. It's science. You need to approach it that way. Exercise science, to be exact with specific goals.
On a side note, yesterday on theheart.org there was a study that as few as 7 HIIT sessions can markedly improve AT (much more than steady state cardio). I've been touting it for years, and..it's ultra cool.
As far as the person you've singled out, well, if you see them the worst thing they can say is no (well, maybe beat you up, etc.). It's all about perception of where the other person's head is at. Yes, gyms, are cruisey...lots of gay / bi guys go to them (for obvious reasons like GETTING AND STAYING IN SHAPE), and there are times where folks are more approachable than others. You need to be sensitive to that. You also need to learn to study on your own, put on your big boy pants, and...be a real boy.