Since the release of the last Harry Potter book, we know that R.A.B. stands for Regulus Arcturus Black, brother of Sirius Black. R.A.B. removed one of Voldemort's Horcruxes from its hiding place.
by DefinitionMaker September 16, 2007
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Acting in a regretful manner, or to be full of regret following an action.

Comes from the phrase, 'rab-regret'.
Look at that feeble man doing the walk of shame. Bet he's rab-regretting that.
by Vikram Ramsey December 22, 2010
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The person who took the real horcrux in Harry Potter and the Half-Blood Prince, the sixth in the series of seven books. As of now we do not kow who r.a.b is for sure, but fan speculation is running wild that it is Regulus Alphard Black, Serius Blacks' younger brother who used to serve Voldermort.
I personally think that r.a.b stands for two people, with 'a' standing for 'and'
by Honjo Norgen September 19, 2005
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R.A.B (pronounced "rab") stands for Rude Ass Bitch. R.A.B is someone who is known to be nasty and especially shady. It can also be used to describe someone who is just over the top feeling themselves to the point of being annoying af.
Ugh did you hear what Alizaih said about Aretha yesterday?? She's such a R.A.B!"

"Justice stop looking in the mirror you're starting to look like a R.A.B"
via giphy
by Girlwhoknowsnothing November 03, 2016
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R.A.B stands for "Ratchet Ass Bitch". You would probably use this one someone that you don't like. Or someone who is pissing you off.
"Yo. Sara has been acting like a R.A.B recently."
"leave me alone, your such a R.A.B"
by bxlla March 01, 2017
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A Random-Ass-Boner. For instance, when you are just sitting down minding your own business and suddenly you get a boner.
Mark: "Dude I was in French class today and I got an R.A.B!"
Steve: "Ahhhh I HATE IT when that happens!"
by Superdean March 05, 2009
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