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1.
A Really Old Virus (probably form the 70's) which make the host spontaneously dance disco and wear flat heels and start snaping their fingers and saying "groovy"
Person 1: Wanna go Bowling

Person 2: Groovy

Person 1: Call 911, we got a guy here with a retro virus.
by Red Butted Baboon April 04, 2011
 
2.
A virus that has been until recently out of fashion but was brought back by a trendsetter thus making it cool to have again.
Charles Bronson: "Oh man, did you hear Johnny Hurn is bringing back a Retrovirus?"
Stan Lee: "So which one do I need to get? Gonorrhea? Syphilis?"
Charles Bronson: "He's bringing back them all!"
by Alex Johnson(Hotass23) September 17, 2008