Most people won't do it because they hate the feel of hot breath on their face

I HATE hot breath on my face, but if it was with somebody attractive then I wouldn't mind a damn bit.

I refuse to because I like breathing in nice, cool air

I think it's gross

OMG did this bird picture actually become a meme!? I remember when the post of this type of birds with some facts was posted, and someone commented, "This should be a meme!" Dang I'm getting old XD

It's not the carbon monoxide that gets you, it's the morning breath. I don't know when morning breath kicks in because it's there often well before morning, but I reckon it's sometime after the minty scent of toothpaste wears off. So about forty minutes after you've brushed and gone to bed. Seriously at some point in your life you're going to be madly in love, really into someone, worship them even, wake up the next morning next to them, thank your stars that you're so lucky and say "honey, let's do it!" but with the agreed understanding that there's no kissing because you've both got morning breath and are too lazy to get out of bed and brush your teeth. You're like turning your head to one side while you talk in case your morning breath puts them off. You're going to be talking to the wall with the one you love because of this. It will happen.

Actually you breathe in 21% oxygen and breathe out 16%. So unless it's an airtight room, there's no worries. Except bad breath, forget the science, turn around. =)