The last four girls I approached in my university classes have all said some variations of the "I have a boyfriend" line. And I'm not saying they don't all have boyfriends but I'm curious if anyone else who has been having more luck on campuses and classroom settings can shed some light.

If I walk up to a girl, introduce myself and say you're cute let's grab etc.. is that not enough introduction for her to warm up to me, thus quickly saying "I have a boyfriend" to get out of the situation, despite any physical attraction?