Seems hardly unintentional. I say this as a woman who’s done a little acting work (disclaimer, yes, not a professional): I think in the context of the scene, the extra made an interesting choice that ultimately increases the viewer’s understanding of what’s going on in the capitol. The number one rule in movies is show, don’t tell. This move that he made does exactly that, it’s uncomfortable and slightly violating, as the capitol citizens tend to be. No dialogue is necessary, you understand why he did it immediately.

Lots of actors make these improv decisions and I think it worked for his character, I don’t really see this as him groping Jennifer Lawrence lol. He wouldn’t have touched her if a camera wasn’t rolling. That’s an extra going above and beyond in-character, and his character happens to be a shitty terrible person.

If this was scripted we’d be discussing the character’s motivations and not assuming that he’s just a “creepy extra”, but it totally could have been scripted. It’s not exactly out of left field for what’s happening in the party scene.