Something tasteless or intellectually inferior that is devoid of any intelligence - usually in pop culture. Lacking in refinement and good taste. Often but not always appealing to the absolute lowest common denominator.
"Sorry, Charlie - the second the silly sound effects and music with the low-brow humor start, I'm out the door. No primetime TV for me!"
This is used to refer to the rare kind of "bro" that is able to pick up on some low brow obscure reference that you occasionally cleverly come up with.