Like most other blatant logic that he couldn't argue with--it shut Barney the hell up, making his face crumple and contort in aggravation and quiet disgust. Either with the fact that he didn't have the supporting evidence for argument, or had just run out of crude, harsh things to respond with that he didn't always necessarily mean.
She thought he was a good guy?
"They're called one night stands for a reason, I mean, I meet people at the bar it's not like I'm going out to the speed dating rink or the committed couples for life sanctuary and crapping on dreams." Not that he hadn't initiated similar plays, or damn well known he was sleeping with a girl who would want more, that was part of the challenge for him, sometimes. Cruel as it was.
Barney's aim wasn't to be cruel, he was just thoughtless most of the time, to a selfish degree. He didn't think outside himself or the small, tight knit group of friends he had. That was too complicated.
"I'm not a pedophile or a rapist, jeez I mean. I like women. I'm a dude, dudes like women..except when they like other dudes, which is cool, but I didn't get that gene. I got the liking lady gene so there."
But Tracy had a point. After all, the girl he had supposedly caught the feelings for didn't take him seriously, and it was...all his fault. He'd potentially ruined his own chances. And when he realized that, he shut the hell up again.