There are plenty of different ways to describe someone who's interfering in a situation where they're not wanted - or, as it's sometimes known, "poking one's face in". Synonyms might include "butting in", "sticking your oar in", or "nosying around". In other contexts, "meddling" or "interfering" might be more appropriate - particularly if the person involved is trying to control or manipulate a situation rather than simply being inquisitive. Whatever term you use to describe this kind of behaviour, though, the important thing is to recognise when you're doing it - and to try and step back and let others handle things their own way, whenever possible.
