I learned this one the hard way back in college, I had a bunch of classes with this cute girl and we started hanging out daily, I even got her to come out for a drink, then when I asked her out again she told me she couldn't because she had to clean her apartment !
I then knew something was up but we still had classes together and then it started, ex this, ex that, it was all she cared about. We were also facebook friends, she would go to a bar for 2 hours yet upload 50+ pictures of herself at the bar (weekly!), all to try and make the guy jealous. Thats when I clued in, the semester ended and I never saw her again.