What is Missioning?
1.
To be totally focused on one goal whilst under the infuence of narcotics, to the possible detriment of personal health, social standing and other shit.
"Nah, leave him be, he's missioning for some Rizla and won't be back for ages."
2.
Using the public transit to go someone's house/to an event
"Hey are you guys going to Franny's?"
"Yeee, bro. We're missioning it there."
"Seriously?"
"Shelay"
See