A 'tailgate' is the back part of a truck or heavy goods vehicle. Drivers who stick too close to the back of another vehicle were said to be having a 'tailgate party', which was then just shorted to 'tailgate'.
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Andy Maio invent this phrase in the early 70s
From a Laurel & Hardy movie.
fROM DA TOIleT
From the Hood thats how we do. Aight its all good
Greece
Right now we think of tailgating with football. I believe that it started with soccer, they have crazy fans who would hang out around that stadium.
latin
The Bible
from joey in friends
stop
1820-30
from girls ...to hissy...
in concord and lexington.
England
facebook entry
Andy Maio invent this phrase in the early 70s