diggi is a more acceptable, friendlier way of saying "digga".
it's often used to show your friend that they fucked up something or acted stupidly.
example 1)
"hey man, where are you?"
"diggi, i said that we'd meet later. god damn."
example 2)
"mate what the frick are you doing?"
"just.... idk layin' here, smokin' stuff. you want some?"
"diggi.... it's TUESDAY MORNING"