As a noun, this phrase is a positive way to identify a pothead.
As a verb, it means to spend a long amount of time to smoke as much weed as you want/have. This is a good way to chill and find yourself again.
History: This phrase is based off a radio host who is AKAed as Captain Robby. His actual identity is unknown, but it is known that he enjoys fun times and PB&J sandwiches during said times o' fun.
Noun: "Dude, you're such a Captain Robby, I love it. Got any extra pot on you?"
Verb: "Hey, man, I'm thinking about 'captain robby'ing it tomorrow. I just need to relax, I'm too stressed, I need just one day where I can smoke as much weed as I want."
Other: "Make me a peanut butter and jelly sandwich, and bring it down to the station and win our grand prize!"