Green’s Dictionary of Slang

frap v.

[note dial frap, to strike, to beat]

a euph. for fuck v. in various senses; also as n.

[US]Boston Globe Sun. Mag. 21 Dec. 7–8: After the junior promenade a student is said to be ‘frapped’ if he has been staying up nights to attend the festivities.
[Aus]Sydney Sportsman (Surry Hills, NSW) 27 Apr. 3/6: Some fatuous, fathead fish-frapper writes to‘ 'John Norton. Esq’.
[US]Eble Campus Sl. Fall 3: What the frap is going on?