Wiktionary
vb. 1 (context intransitive English) to leave school early 2 (context transitive British slang English) (''followed by '''with''''') To successfully engage the company of someone for a period of time.
Usage examples of "cop off".
The cornrows jerked, and the body bucked wildly, catching the wrestling cop off guard.
Moody could have made use of police transport, but he didn't want to pull some cop off duty just to run him to the station.
At this hour, the only customers were two elderly ladies and a cop off duty.
There you had a chance to cop off a nice bunch of coin on that fight and instead you kill it for yourself and everybody else.
It was easy to arrange to be one of the blokes-the slags weren't at all shy about inviting their male colleagues to join them on their riotous nights off, and if you stuck with them all night you were absolutely guaranteed to cop off with someone-but there was a price to be paid.
You say they told you down at the typewriter joint that you was the real cheese and ought to hold any job you could cop off.