Weird sex faces are a lot like weird sex noises: they work lovely provided they are genuine and don't remind your partner of Ace Ventura or Jerry Lewis. Well, let me preface that. How weird is weird? Are you pulling your lips over your nose and crossing your eyes? Are you making a chubby face with your cheeks and smiling manically at your man during intercourse? That in fact should be curtailed.
But for the most part, Weird Face in the heat of passion can actually be a plus-- it's your body's way of saying I'm all in. I'm immersed and lost in sensation. Remember most people complain they are having sex with a tombstone, you're offering your mate ... electricity and something to look at. But again, make sure it's authentic. There's nothing worse than looking down and knowing your partner is faking a freak out. So I've been told... by me.
But back to you, don't worry your weird little sex face about this. Sex is all about expression and individuality. I'm unclear what Sex Ed. class or 16th Century Vatican pamphlet you read that has you thinking sex should be quiet and controlled. It shouldn't. It should feel like a circus with you being the ringmaster, lion, clown and trapeze artist.