Creative writing for 12 year olds

When is it appropriate for a man to write like a 12 year old, and say "OMG"?

I think if I saw a devastating mushroom cloud on the horizon. Maybe....

If I witnessed a school bus full of children get scooped up by a tornado, I might say Oh my god.

But if I saw a funny picture of a cat with its paw on its genitals, I don't think I would say oh my god.