also: なんぱし
noun
pick-up artist; masher; skirt chaser
A man who habitually approaches women in public to flirt or ask for dates, often with a negative connotation of being insincere or persistent.
あのナンパ師は毎晩渋谷で女の子に声をかけている。
That pick-up artist hits on girls in Shibuya every night.
彼はナンパ師みたいに何人もの女性に同時にアプローチしている。
He's approaching multiple women at once like a skirt chaser.
From ナンパ (pick-up, hitting on) + 師 (master, specialist). ナンパ itself derives from 軟派 (soft faction), originally referring to a group favoring non-confrontational approaches, later associated with men seeking romantic encounters.