A sexual act in which a man, when he's nearing climax, puts on a wig of dreadlocks (This has the best effect when the wig comes on while her eyes are closed, so she gets the full effect when she opens her eyes.) And just as she's thinking "What the fuck?" you pull out and cum all over her while singing the "Oy yoy yoy. Oy yoy yoy yoy. Oy yoy yoy, yoy yoy yoy yoy yoy" section of the chorus of Buffalo Soldier by Bob Marley.
Used to be a term for black American soldiers in old USA, now can be used to describe a stoner / pothead who like to smoke the magic herb while listening to reggae music all day long.
Check out Bill here, a true buffalo soldier. Would be smoking mary jane all day if he could.