When you are violently ill and uncontrollably vomit and have explosive diarrhea simultaneously. The victim is usually unprepared and in midstride for the bathroom when it occurs. Also known as burning the candle at both ends.
"Dude, I just caught my mom and dad going at it in the car! I almost number 7'ed right there!"
"Man, I was so sick, I took a number 7 and there wasn't any warning!"
"Dude, you don't choose when to number 7, number 7 chooses you."
"I don't wanna talk about it..."