In pro-deo it refers to applying deodorant to the forehead.
It's considered highly uncool to NOT put deodorant on your forehead guys!
Juno: "Yeah iMean he was being such a jerk that day."
Junebugg: "Wow Don't worry. I'm sure he wasn't pro-deo."
Juno: "You're right. Not even cool yo."
-If you aren't Pro-Deo, then you're not qualified to date Juno or Junebug ! :)