Hello to everyone.

My friend has a funny description on his Skype: "Good? Bad? Well I'm just boy with gun.". I'm curious of missing "a" or "the" like "a boy" and "the gun".

Would somebody be kind to tell me why or why not?

Have a nice day!
My suggestion would be that your friend made an error. I'm just a boy with a gun. Both nouns require the "a."
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Hi, GG. What do you call "just" in the sentence grammatically?
Perfect! Thank you!