Tone ofvoice, expression in his face when he said it, the immediate energy in the room after that was said...There is alot to consider here 🤔 The fact youre asking this question though makes me feel worried.
my two cents!

I think that's his way of flirting with her.

Yeah, he’s saying stop it nicely

I think it all depends on what that means to the guy. If I say that, I'm not telling her to stop anything. I think the only person that can truly answer that and get the correct meaning is from him. The sound of his voice and his body language may even play into deciphering it correctly.

That depends on a literal ton of possibilities, but if it were me it could mean either that I think your flirting is annoying, that I think you’re completely bonkers, or that I think you’re cute as a button and would love to ask you out 🤷‍♂️

it may be Him.suggesting that he thinks he is unworthy "it would be silly for you to be interested in the likes of me"
Or the opposite

I think he was being silly and flirty towards her but who knows anymore.

More like he doesn't believe it for real and just cross checks her if she's doing it.

Maybe her means of flirting are absurd.

He may have a DDLG fetish and is treating you like a silly LG…

He’s politely telling me that he’s straight.

Probably likes you

He likes you

Yep pretty much. He no like and is making it plain. I do this when I want them off my back but include they're a 'friend' at the end. It let's them down easy.

It depends on the guy entirely. It all depends on what that means to him. We're not all the same.

Depends on tone of voice, though I wouldn't say that unless I wanted to shut it down.

Either that or he is flirting right back. Depends on the guy.

That sounds like a rejection...although it's hard to know for sure.

He's not interested.

Gay

Or being socially inept

No he likes it😋