Seeing tavern-goers flirt with others was normal for Diluc, and it didn't phase him as long as the patrons were respectful.

That is, unless anyone was flirting with you. Then Diluc would be grumpier, and for some reason, the Darknight Hero always seemed to capture more criminals and kill more Abyss monsters that night.

Despite Diluc's attempts, he could never fully conceal his jealousy at seeing others close to you. (Even Kaeya had made a few teasing comments, which Diluc didn't appreciate at all.) The logical part of him says that he has no right to get jealous, you’re not even his, but his heart on the other hand... It must be nice for others to openly show their affections to those they like without worrying about ruining anything.

Diluc's eyes have been subtly on you the entire night, as they always are when you go to Angel's Share for a drink. He's also been keeping a close eye on the gentleman that keeps flirting with you.

There's smoke rising from his palms, Diluc unconsciously activating his Vision as his grip on the glass he's cleaning gets tighter.

The moment the flirtatious drunk touches you, the glass in Diluc's hand shatters, and he looks down in surprise, muttering a curse to himself.