I have a problem with reading men. When I go out, I have a difficult time telling when dudes are potentially interested in me. Often times, my friends have to explicitly tell me someone is flirting, because if they don't, I will never notice until some guy has his tongue down my throat or some other appendage in yet another orifice. Maybe part of the problem is that when I go out, I go out to have fun with friends and I'm never really "on the prowl," as it were. But, back to my main question. What are some explicit signals that I can look for?
See, the weird thing about men is that they are all individuals who do and say different things, almost like how people are. I'm not sure that there is a universal answer to that question, outside of the tongue-in-orifice metric you have already established.
I mean I guess my question to you would be about what you're looking for. I'm not sure I see where the problem is with you just going out to have fun with friends and not being on the prowl, if you are enjoying doing that. Maybe you have trouble picking up on people's flirtatious signals because on some level you could give two shits about a random guy trying to pick you up when you could be hanging out and drinking beers with the people you like.
Anyway, I guess if you're writing me you are unhappy with the frequency you get laid, so I will say that in general, if a stranger is talking you at a bar in a way that is not utilitarian (i.e. "Where's the bathroom?" or "When she comes by will you order me another beer?") or clearly the kind of basic politeness that some naturally chatty people employ ("Wow, sure is a long bathroom line, huh."), then it is reasonable to assume that they are flirting with you.
One thing about bars is that so much depends on the time of the evening/drunkenness of the crowd. If it's early and someone is asking you questions about yourself and listening intently, that is probably flirting. If it's late and someone is boozily yelling shit at you about how that one dude from work is such a dick, that is probably just a drunk guy being an idiot. But you know, drunk guys being idiots would probably sleep with you too, if you were at all interested.
What I'm saying is that it's probably safe to conclude that any stranger who takes an interest in chatting with you in a way that is outside the bounds of basic polite human interaction could be flirting, and you will only know for sure by continuing the conversation/sticking a tongue in one of his orifices.
I do urge you, though, to consider your own motivations for going out. I know lots of times when I was single I felt like 'Wow, I really shouldn't pass up this opportunity to get some', but actually I was having a completely fun time with friends. Especially if I was a single person with some non-single people, I felt like a weird pressure to find someone to go home with, not because I was like "Oh I have to be in a relationship too", but sort of this weird vicarious desire for carefree sex fun from the coupled, like: I can't go home with strangers so I really think you should take advantage of the fact that you can. It is ok to not want to fuck anyone sometimes. Just, you know, saying.