When you are having sexual intercourse with a female and you make her squirt all over you because you hit her sweet spot several time. Usually when this happens, her legs will start to shake rapidly and she will grab you very firmly. This is called juice boxing because youre usually beating the vagina up for several hours and she has you soaking wet in result.
Nate was juice boxing her last night. I could hear her screaming from outside the room and he claims she was soaking wet and blasting all over him.