This phrase means "let me
puff half of your cigarette." If someone doesn't have a cigarette, and you are smoking one, then they will request you
to buzz them down, meaning let them puff the
leftover half of your cigarette after you are done with it.
Bob : Yo, you got a
bogie?
Pablo: This the only one I got, man.
Bob:
Buzz me down, son!
Pablo: aight,
wait up