Someone who 'acts' as if they are completely superior towards/around another person.
Someone who's of the perception that they are 'better' (physically and mentally) than another.
"Yo, if you wanna roll and chill tonight we can do it, but don't try to be actin' all sadiddy around my homies"
"I am not goin' to the club with HIM","Stop bein sadiddy and lez' go."
"Girl why you actin all sadiddy in the club, telling yo chicks you dont know me?"
"No way girl, you dont wanna go for that dude, he all sadiddy, droppin chicks faster than stacks"