To masturbate; to stimulate one's own genitals to achieve sexual release.
2.
SpainLatin Americacolloquialinformal
Figuratively, to indulge in self-gratifying or pointless fantasies or activities; to engage in self-indulgent behaviour that produces no constructive result.
Examples:
ES: Primero, era bizco y después, de tanto hacerse pajas le enyesaron también una pierna.
EN: At first he became a one-eyed person then jerking off more and more they had to put his leg in a plaster.
ES: Mira a tu mamá, ...a fuerza de hacerse pajas, ya no sirve para nada. - ¡Déjala!
EN: Your mother, she has worn herself out touching herself, it's so that she's nothing down there.
ES: Son revistas para hacerse pajas.
EN: They're stroke books, stupid.
ES: - Para hacerse pajas.
EN: - Jack off movie.
ES: No es el juego de hacerse pajas, ¿no?
EN: It's not that wanking game, is it?
ES: ¿Y esto qué coño tiene que ver con hacerse pajas?
EN: What the fuck does any of this have to do with jerking off?
ES: No se quién era este tipo, Sid, pero tenía un gran gusto para hacerse pajas.