What does “пофлексить” mean in Russian slang?

Пофлексить is the perfective of флексить — “to flex,” borrowed from English and bolted straight onto a Russian -ить infinitive. It means to show off, to posture, to perform toughness for an audience. The -ить ending is the standard runway for English verbs landing in Russian: гуглить (to google), лайкать (to like), стримить (to stream) — the language absorbs the stem and conjugates it like any native verb.

In the clip, three friends start an Instagram livestream “чтобы пофлексить перед камерой” — to flex in front of the camera — waving an airsoft gun and throwing gangster poses. Their performance ends abruptly when the host’s mother walks in with a belt. The perfective prefix по- implies a completed bout of showing off, a nuance that fits the scene perfectly: they flexed, briefly, and then paid for it.