noun
person who is still a virgin after turning 20
Slang abbreviation of やらずにハタチ (yara zu ni hatachi, 'turning 20 without having done it'). Used in casual, often self-deprecating or teasing contexts.
もうすぐ二十歳になるけど、ヤラハタになりそうだ。
I'm about to turn 20, but it looks like I'll be a yarahata.
彼はヤラハタを卒業したと自慢している。
He boasts that he's no longer a yarahata.