what does it mean...

[WannaBurger2016]

....when somebody replies to a post with just a ?

Wanna, apparently it all started some years ago when Gordon Brown was invited to participate in a Mumsnet webchat. Someone asked him which was his favourite biscuit and he refused to answer - or kept saying "no comment". So the 'no comment' smiley became part of MN lore.

It's now used as a quite derogatory 'non answer'/no comment'.

Ahh thank you, that makes sense.

Offering someone a biscuit seemed to me to be a very nice thing to do. Couldn't reconcile that with the context that suggested there was something passive aggressive about it!