When you are having sex and are near the end, you or your partner stop suddenly and run to the light switch, flicking it on and off while yelling "Bonus Round!"
The you go back and have sex harder than before.
Ulzzang true definition is "best & "face" = best face in korean. They are basically people with above average looks, sometimes with the use of photoshop and haduri who post their pics online, some becoming internet celebrities.
"Hey, see that chick over there? She's pretty enough to be an ulzzang. :D"