Green’s Dictionary of Slang

1. a hijacker.

1972

G.V. Higgins Friends of Eddie Coyle 86-7: ‘Who else was on that job?’ ‘A bunch of other tailgaters.’.

2. one who drives too close to the car in front.

2001

(con. 1964–8) J. Ellroy Cold Six Thousand 99: Wayne saw a two-car crash. Pete said, ‘Fucking tailgaters.’.