Possessed

So, the SiQ posed a question last night, which I am ill-equipped to answer. Therefore, I'm posing it to you, as I find it to be a common occurrence -- well among the two of us anyway. So, here's the deal. There's this guy, we'll call him Lester, that she works with, who's nice and entertaining enough, but not on the list of potentials -- although not for lack of trying. He's just not on her list. So anyway, she still jokes around with Lester, because that's what cool chicks do. Apparently, earlier this week, she was joking around with a different guy, we'll call him L'il Bro. So, L'il Bro was being a smart-arse, cuz that's what little brothers do. Apparently, Lester asked the SiQ if L'il Bro was bothering her. To which she said "yes". Bear in mind, that this is a group of smart-arses who are accustomed to joking around. The next sound we hear is L'il Bro's body being slammed up against the wall (albeit gently) and L'il Bro saying "sorry man, I didn't know she was your girl". Please note, at no point in this post did I declare Lester and the SiQ a couple.

Now, slightly similar situations have happened to me, and certainly to other women. Thus laying the foundation to the question. Why are the men on the not-potential list so darn possessive? And how do you tell these men that they should lay off -- particularly if you don't want to hurt their feelings? And, given the numerous Dateline specials on psychos, how do you determine if the possessor is psycho and avoid being stalked? Any ideas? Anyone, anyone? Bueller? Ok, I'll be waiting for your answers. Thanks. :)