That's the thing about girls. Every time they do something pretty, even if they're not much to look at, or even if they're sort of stupid, you fall in love with them, and then you never know where the hell you are. Girls. Jesus Christ. They can drive you crazy. They really can.

This quote is referring to the effect that girls can have on people. Even if they don’t look great or they aren’t very intelligent, they can still cause strong emotions to arise in people. These feelings often catch people off guard, and they don’t know how to react or what to do. The quote also acknowledges how confusing and overwhelming it can be to fall in love with someone, especially when it’s a person that you didn’t expect to fall for. The speaker of the quote recognizes the power that girls have and expresses his frustration about it.