to think that there's no way to say...

[WingsofNylon]

the words 'I am an adult' without sounding like a child?

Or a teenager at best?

Wear a lot of tweed, grow a moustache and have a pipe in one hand and tumbler of scotch in the other whilst sitting in an antique chair and then say it.

I've never said those words - or thought them to be honest
I'm going to try and slip them into conversation with someone now

Ha ha, same, next time I want to express my opinion about something, I'm going to start "As an adult, I think...". For example, "As an adult, I think that we should go for the stuffed crust"

Ha, yes! Next time I'm at the local off-licience I shall say ' as an adult I would like a nice bottle of red'
Can't wait to see the reaction I'm so easily pleased

You can to a toddler.

'Because I'm the adult, and you're my son and you have to do as you are told. You can drink from your own toilet when you are an adult.'

glittertits
Yes, that's pretty much the only time. And it wont be long before they wont acept the argument.

or even worse 'I'm a grown-up'.
I do say it in a jokey way occassionally, usually when i've bought some kind of domestic good e.g. 'I feel very grown-up, I now have two types of baking tins'

Prawnballs did you try it? The only time I do use it is in a jokey way to justify doing something a bit odd.

Last week, DP says 'fancy some breakfast? ' Me 'yep and it is going to be ice cream because I am an adult.'

I haven't been to the off-licience yet

I'M 26! STOP treating me like I'm 24!

I say it all the time

Normally something like 'I'm going to sit on my arse and do nothing except eat crisps, you can't stop me because I'M A GROWN UP YOU KNOW!'