Where would you cross the line between "being too drunk to allow consent" and "regretting that night"?

I have read from somewhere (maybe it was Bitch's Guide to Etiquette on Tumblr) that there is a differene between a person being tricked into sex from being too drunk to properly give a "no", hence making it rape, and a person who got a little too drunk but was able to freely choose to have sex and regret it in the morning. What is the difference?