I think it's a common courtesy to ask first, but there are plenty of people out there who don't! I often get odd looks if I don't let DD have certain foods - there's plenty of stuff she's not had yet which people think is common place to give to kids (lollies, cordial, soft drink, etc!). I am getting a bit more lax now.

I get annoyed with MIL occasionally (although not so much now) - at prob 4 months, she gave DD a choc hedgehog to have a suck on, and has let DD finish the dregs of her coffee! The worst thing she has done in regards to food wasn't to DD luckily - at a school fair, she gave a stanger's toddler sausage rolls and kransky's - the mother had to come up and ask her to stop giving her toddler food! That was a bit too far!