Well - it happens enough for 153 messages to be posted !!!
No one's got THE answer - from being polite, to, the old fashioned "shut the f*ck up will you ".
It exists and that's the end of it - no universal solution - just take all occurrences on an individual basis, as, some are more annoying than others.
Know it's going to happen - without thinking it shouldn't happen.
It's irritating at times ,but don't forget it's sometimes proficient musicians playing along - stealing the thunder of the less talented individual who started the song or tune, which is the unwanted accompaniment - not as most of the thread supposes where duffers spoil good players. A thought........
Cheers