A lengthened version of btdubs, which is a legnthened version of btw, meaning "by the way". Btdubstep actually has more characters in it than "by the way" does, if you aren't counting spaces.
Dude you look like a model. That's a good thing, btdubstep.
Die Mails werden von firstname.lastname@example.org versendet. Wir versenden keine Spammails.