It comes from the spanish word "maceta" which means "vase or pot for flowers and plants". The act of planting would be "macetear", which can be a synonym for jerking off in spanish. And so, someone who jerks off a lot can be called "macetein".
"Stop masturbating!, don't be a macetein"
"Stop rubbing your crotch! Damn, you're such a macetein ¬.¬"