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2.
IRB
Irish Republican Brotherhood. Father of the IRA. Greatest heros of all time, dared to challange an empire and and slowly but shurly won. Unlike those IRA fuck ups who need to step down. This is the 21st Century and peace can be achieved.
IRB kick British ass.
by Red Hot Chili Pepper September 09, 2003
 
1.
IRB
Short for "International Rugby Board," the world-governing body of rugby union. The IRB is responsible for international matches, rankings, and keeping team managers in check. Similar to FIFA except it's actually effective, not run by complete idiots and hires competent refs.
If it weren't for the IRB rugby would be a clusterfuck. Just like FIFA.
by Matt..... June 24, 2010
 
3.
irb
"i r back" - "I are back", the less grammatically correct way to say "I am back."

The follow-up to brb, "be right back".

Used in IM conversations- or real ones, if your friends are that blind and you're too lazy to speak in complete sentences.
A: Guess what?
B: brb
A: Gah.
- 10 minutes later -
B: irb, what'd you want to tell me?
A: ...crap, I forgot.
by i r back lulz August 17, 2009