Abbreviation for "Subscription for Subscription" on video-featured websites such as "Youtube.com".
Sub 4 Sub is a request to subscribe to your profile with a guarantee to subscribe to the subscriber's profile.
Essential for nerds with small self-confidence.
intelligent youtube-goer: No one cares about your meaningless subscribing account. Just shut up!
isubscribetoyou: *cries and goes to another video or channel in the hopes of getting subscribers but fails miserably*
to say "sub4sub" to another user means that if that user will sub (subscribe) to your videos, you will sub back to theirs, It may sometimes be posted as a comment on any random video to be pointed towards any user that's stupid enough to get sucked into it, Many sub4sub's are ignored, or marked as spam
"Dude, GTFO, no one wants to sub you, your videos suck anyways"
RegularUser2: No, your videos are horrible, and I don't need to sink to your level to gain subscriptions.
RegularUser2: You have no videos. Why would I subscribe to someone who doesn't have any videos? You are a failure.
Customer 2: Hey, sub4sub?
Customer 1: Yes, of course!