がん～

ガン is a slang prefix meaning "hard, all-out, totally". It goes on the front of a short noun or a ます-stem, and the word it makes takes する like any other する-noun. It is usually written in katakana, sometimes as がん.

You hear it on a limited set of words. The most common are がんみガン見(staring hard) and がんむしガン無視 (ignoring completely), with がんガンなき泣き, がんガンね寝, がんガンせめ攻め and がんガンきき効き after them.

Register

This is casual speech among friends and casual writing online. It does not belong in polite speech or anything written for work. The everyday words are じっとみるじっと見る for ガン見 and かんぜん完全にむし無視する for ガン無視.

Usage notes

These go beyond the する-verb.

As a noun

Without する, the word is a noun and takes で or だ like one.

ガンを飛ばす

がんをとばすガンを飛ばす, "to glare at someone", looking for a fight, is an older expression with its own ガン. It is not the prefix.