1)To reject a statement/idea/proposal from a wasteman and to encourage said fool to look at himself and man the fuck up.
2) To cast a downing judgement on a fool's actions.
Wasteman: This party sounds hectic but I say we go to my nans, she cooks up a mean steak casserole.
Safeman: *kiss gums* Blud you trippin, disallow yourself.
Wasteman: Aight, Halle Berry would get it, but if you catch Rosie Odonnell from the right angle, I swear to ja I would happily poke her.
Safeman: Be easy nigga! step down. Think 'bout wha chu sayin' foo'. Dat bitch is stacked out. Disallow yourself.
Wasteman: *Gets his ankles broken in basketball match*
Safeman: 'memba I told chu, tell your friends and disallow yourself.