When you watch a video on youtube then it leads you to another one, and another one, and exc. by the time you realize it, you cant even remember what the first video was.
"hey what r u doing?"
"watching Justin Bieber getting hit w/ a water bottle on youtube"
"WTF? how did u get there?"
"haha youtube hangover!"
The aftermath regret of starting or jumping into an argument on Youtube, and paying for it by getting destroyed with hate comments and/or death threats in the morning.
"This kid on this video just said 'Skyrim blows' and he just got RAPED with hate comments. He's gonna have one hell of a Youtube Hangover."