This can be tough but if need be just use you hand to slap you flacid penis around the vagina area.
When the girl is pissed off that you could not get it up you must use the excuse that this is how they have sex in europe
Boy: what doesnt that feel good?
Girl: Your not even hard at all
Boy: Of course im not, im doing it european style, i thought it would be kinky to try something different, but clearly im sexually on a different wavelength to you,
Girl: Who told you that was european style sex you have never been to europe
Boy: your fat get out of my bed