I think it can go either way, although one story comes to mind.
I meet a girl at a bar. wearing button up. get her phone number. we go out once a week later, i k-close.
i see her at the gym the next day (never seen her there in my life prior) - I am wearing a tank top. not really a ribbed wife beater, something like this:
http://www.dogfunk.com/images/items/900/HUR/HUR2256/CYA.jpg - she says, holy ****, i didn't realize you were so ripped or something. calls me that night, we go out for drinks and I f-close.
When I go out with the bros to a bar, sometimes i wear board shorts and something like that tank. I have close a
bunch in tanks like that and surfer-ish looking outfits. It's an easy way for me to show off my hard work in the gym, and NOT look like a guido. fortunately this is acceptable where I live. In NYC for example, not acceptable.
dates, even for just drinks, i rock the button up. sometimes a fitted lacoste shirt works well too for an in betweener situation. lacoste has the shortest/tightest arms of the polo type shirts and fit my chest and arms tightly, so that works well too.
In short, i don't think it really matters, but showing off what u got if you have it literally never hurts.