Green’s Dictionary of Slang

a woman (or man in a homosexual context) who appears to be offering unrestrained sexual favours but stops short of intercourse, leaving the male partner frustrated.

1944		in G. Legman Limerick (1953) 351: There was a young fellow at Jesus / Who developed a phallic prosthesis. / He made use of this tool / To thoroughly fool / All girls who were known as P.T.’s’s.
1966		Trimble 5000 Adult Sex Words and Phrases.
1974		(con. 1940s) E. Thompson Tattoo (1977) 42: She’s the biggest little PT in town.
1980		Maledicta IV:2 (Winter) 199: Of course, one might meet a prickteaser (p.t.) who refuses a present for a good girl.
1989		P. Munro Sl. U.