Look after your brother, ya idjit.
"Idjit" is an affectionate, but exasperated, appellation applied by Bobby to Sam and Dean - first heard in 3.03 Bad Day At Black Rock. It has become something of a catch phrase, and Bobby's use of it is imitated by Crowley in 6.04 Weekend At Bobby's.
In 7.10 Death's Door, Bobby's dying word to the boys is "Idjits", said with a smile.
Jim Beaver refers to the followers of his Twitter as "Twidjits".
Idjit = idiot. It is a southern thing.
See also Nicknames