Just a cooler way to say BTW so that you don't look like that nerd using all the lame acronyms. If you used BTW before then you can change and instantly regain respect. True story.
You: Stephen, I got this new----Oh BTDubbs I madebrownies!
A spoken slang for BTW, meaning "by the way", which originated on the internet. Rather than say "bee-tee-double-u" out loud, people began saying "bee-tee-dubs", which became "btdubs" when translated back to the internet.
Pronounced "bee tee DUBS", a spoken form of the acronym btw which stands for "by the way."
It makes little sense, as the term itself has as many syllables as the phrase it's meant to abbreviate. Accordingly, it's degenerated into a cutesy term used mostly by girls. It has also been used in the gay community as a candid way of letting others know you are a bottom.
Jason: That's a very cute outfit you're wearing, btdubs.
Bruce: Great, I'm a top. See you at my place at 9?