Means to cut corners, save money, or basically be a cheap ass
Chetan ask his boy Minkus if he was going out saturday night, Minkus replied "nah bro i think im going to just going to be jainin' it at home."
Means to cut back, save money, or simply not do anything.
Chetan asked Minkus if he wanted to go out tonight, Minkus replied, "nah bro ima jainin' it at home today."
A person who's down for NOTHING.