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1.
nickname for anybody with the last name stein

usually used as an insult to said person

playing off of the disease swine flu

can also be used when talking about something the person with the nickname steinflu is doing
what up steinflu?

hey get away from my food i dont wont to catch the steinflu!
by hsquared1/64 October 23, 2011
 
2.
a beer hangover
He's not sick, I left the bar at 8 & he was pounding down the beer then, he must have got a dirty mug after I left & up & caught the stein flu.
by elpasospike November 09, 2009