You can't usually tell just by looking at a potential friend (male) whether they're going to be a perv or not. You don't know who's going to start pursuing a fling until you talk to them. Even then they may not reveal it until later.

That's not entirely true, at all! A guy and a girl can be just friends, even if the guy finds out the girl has a boyfriend after, oh I don't know, a week or two, just to throw a figure out there. You can easily talk to a guy (assuming he doesn't hit on you or try anything) without mentioning your SO. If the boyfriend doesn't come up in conversation right away, he doesn't come up. That's not always a bad thing. Maybe they're discussing what's going on at work. Maybe something happened. Maybe, like the OP said, they were sharing amusing stories. Not every guy is interested right away, if at all, so it's not always necessary to mention it. I've seen a girl mention it one time, and the guy wasn't interested at all. He interpreted it as, she was trying too hard to look cool. He didn't believe she really had a boyfriend, because of that. FYL, OP, for meeting a douchebag that soon. He's clearly not a decent guy if he stops talking as soon as the word 'boyfriend' is mentioned.

Rockstatic, you are not leading them on if you don't mention your SO. You are leading them on if you catch them obviously flirting and don't mention it then, or even if they ask and you lie. That is leading them on. As Steph said, if it doesn't come up in conversation, it doesn't come up. And if you mention it completely out of the blue then it can appear like you're trying too hard in some way.

Obviously the dude in the FML is a douche, I think that goes without saying. What I'm saying is that it's rude not to be up front about being unavailable -- sure, the person you're talking to might not be interested, but they might be too. Obviously don't say "oh, by the way, I've got a girlfriend," but find a way to weave it into the conversation, like, "oh, my girlfriend is really into that too." It's just polite not to let someone think they've got a shot when they really don't.

Why would talking to a co-worker be making them think they have a shot when they don't? Yeah, ok, if it was on a work night out or something. But talking during a tea break or whatever, that's not implying that anyone has a shot, that's being sociable. Like Steph said, within a couple of weeks you probably should have found a way to wind it into conversation, like you say. But not necessarily within the first day or two.

76 - Not every guy assumes that he's got a shot with the new girl at work. They may have a girlfriend of their own and simply just want to talk to her. You make it sound like the guys at work ALWAYS think they have a shot with ANY girl, no matter who's dating who. Whatever happened to making new friends? Or, is that just out of the question nowadays...