When you have sex with a girl and you completely ignore her for the first half and look away. Then all of a sudden you look straight into her eyes and scream at the top of your lungs. The desired effect is that later after you're done she will call her friends and say: "OMG did your boyfriend do this? because he scared the shit out of me when he did that."
A girl gets scared by her boyfriend when he screams at her during sex after ignoring her and looking away for most of the time. That my friends is the OMG Factor.