a pervert (= a person whose sexual behaviour is considered strange and unpleasant by most people)

Stop looking down my dress, you perv. 不要盯着我的连衣裙下方看，你这个变态。

to look at or behave towards someone in a way that shows sexual interest, and that they or others find unpleasant

She caught him perving at/over a picture of a naked woman. 她逮住他正在色迷迷地看裸体女人照片。