When someone disapproves of the way someone else is living their life, they often say "at least I can sleep at night." The implication is that the other person is, deep down, so overcome with life dissatisfaction, usually because of guilt over some moral atrocity, that they can't even get to sleep.
This is rather dumb.
There are a lot of good reasons to avoid sleeping at night. Let us start with the obvious: Boning someone you care about. But there's also staying up all night chatting with someone you care about. There's staying up thinking about someone you care about but can't be with at the moment. There's staying up drinking and partying with friends who are just such good company that sleepiness gets pushed to the side. Hell, there's even staying up playing some horribly addictive video game, or pulling an all-nighter to make up for the procrastination brought on by the same wonderful things that prevented you from sleeping the night before.
Ain't nothing wrong with any of that. "At least I can sleep at night" might as well be "at least I have nothing better to do with my time than lie around doing absolutely nothing for 8 hours a day."
See also: Sleep Sucks.