Rock the mainline
To get "high" on heroine through the means of an introvenus-needle. I.e. - Shooting up.
Addict: Yo, dog... Yo got the shit to lemme rock tha mainline?
Dealer: Fo' sizzle ma nizzle, that'll be fiddy.
Dealer: Fo' sizzle ma nizzle, that'll be fiddy.