Green’s Dictionary of Slang

tailgate v.

[SAmE tailgate, the tailboard of a truck or wagon]

1. to drive a car closely (too closely) behind the one in front; thus tailgating n.

[US]M.W. Frazier ‘Truck Drivers’ Language’ in AS XXX:2 94: TAILGATING, ger. Driving too closely behind the vehicle ahead.
[UK]P. Theroux Picture Palace 44: In the car, tailgating some retired gent.
[US]S. King Christine 58: I goosed the accelerator again, and this time I almost tailgated Arnie.
[US]P. Cornwell Cause of Death (1997) 274: This person’s been tailgating me for the better part of the day.

2. also in fig. use, to follow, esp. of things that are endlessly repetitive.

Times Lit. Supp. 20 May 618/3: Pictures tailgate each other, wall to wall, and floor to ceiling, in the authentic eighteenth-century manner .
[UK]N. Barlay Curvy Lovebox 111: The three Shitskys are behind him tailgatin’ right up his ass.

3. (US campus) to watch women passing by.

[UK]M. Collins Keepers of Truth 75: Driving onto campuses [...] in his fancy car, tailgating and picking up women.