to hate it when people say "Grow Up" if someone disagrees with them?

[HexagonalQueenOfTheSummer]

I think it's such a lame argument/answer.

I've seen it on here several times recently, and on other forums, and people in real life too seem to say it when they can't think of a rational answer or argument.

I really can't see the logic in it; if someone has a different viewpoint to you it doesn't mean they're childish, it means they disagree with you.

Grow up

Who wants to be grown up? I am a bit 38 but mostly 3.

To be fair, some people do hold some ridiculously simplistic, juvenile views.

Yes but often the people who say grow up and spout reams of knowledge have clearly just googled it anyway

Ah yes - google is our friend.

I think you're confused. People will say grow up when they think someone sounds childish, rather because they disagree with them.
HTH.

*rather than

On the whole I think people tend to use it when the other person has said (or typed) something monumentally immature and silly. I can't say I have noticed it used much generally.

It is quite simply rude. Once can only use it in such a context imo

I don't know I think that when posts have gone along the lines of -

"I'm fed up with my toddler standing in dog poo and getting it everywhere"

"Crikey what a fuss, it's only a bit of poo - just wipe it off"

"but it's toxic! So what you're saying is that it's ok if toddlers cover themselves with dog poo and then eat it and go blind"

"Oh grow up"

It's appropriate. Some people do take a perfectly valid point that they don't agree with and then extrapolate in and infer something wildly ridiculous from it.

Any post which contains the words "So what you're saying is...." or "you might as well say...." can often be replied to "oh grow up" because they often say something wildly offensive to both the person who has been misquoted and the general population at large. IMO.