DS is 3, very good speech, chatty, articulate, curious and bright - not saying this to brag but because people may forget he's still only 3 when they talk to him. He does talk ALL THE TIME and often when I'm talking to DH or my mum etc. I may 'indulge' him by breaking off to acknowledge him with a 'yes, that's right' or answer a quick question then resume talking. (I know if I don't he'll just keep on asking!)
If me and DH / mum are trying to actually have a proper conversation we'll tell him 'I'm just talking to daddy now and I'll talk to you in a minute' although this can end in a strop (as does a lot of things). (Trying to teach him some manners but also realising he's 3 and his world still revolves around himself).
However when visiting friends (mainly those without kids) they just ignore what he's trying to say to them and talk over him, usually about the 5th time they will do the 'I'm just talking to X right now'. But then I think they're surprised about how much he keeps on. Which 90% of the time he wouldn't if someone just said 'yes ok' - maintaining several conversations at once is perhaps a bit of a parent skill. This is probably part of a wider lack of understanding (or care! which is fair enough) that visiting adult friends who just stand round talking is very boring for a 3-yr-old. They are enthusiastic about playing with him but only for a few minutes until they realise how repetitive/absorbing it can be then go back to talking!
Obviously all this is normal adult behaviour but I do feel for him a bit when he's trying to join in the 'adult world' (nicely - I don't mean when he's whining etc) and is ignored. AIBU to think if you invite friends/family with a 3-year-old you should make a bit of an effort to get on his level or should he be there to learn that adults shouldn't be interrupted? I realise I sound very indulgent to my child but I'm not really, it's just how I've worded it to get my point across. We're quick to punish actual bad behaviour, too much attention-seeking etc so I sort of think if he's otherwise behaving nicely just constantly talking/asking questions then I don't want to punish that?
On a separate note, when we're at friends, them ignoring him then tends to mean me or DH have to entertain him a bit which sort of defeats the point of visiting a bit! Or perhaps that's always par for the course- one of us always missing out on what's going on to an extent!