Fenris doesn't know why the mage stares at him. It doesn't bother him, really; people have stared for as long as he can remember, which isn't really all that long, but that's not the point. He understands that's he's abnormal. Most people don't glow.
Perhaps that's not the best example.
It's not like he isn't used to it, anyway. Part of Danarius's intent was for the lyrium to draw attention, surely. Fenris was created to be intimidating. Usually when he glares at people, though, they get the point and stop gawking. Glaring does not seem to have any effect on the mage, other than the brief diversion of his eyes for a few minutes before Fenris feels them on him again.
On rare occasions, the bastard will even glare right back. It doesn't bother him, though - the colour of honey certainly isn't frightening, and neither are feathers or poorly-behaved wisps of golden blond hair. Stubble also isn't particularly terrifying, though he imagines it would be quite prickly. Itchy, maybe? Ticklish. It was likely.
Anyway, it's not like he hasn't been constantly surrounded by mages for the short duration of his adult life. This one is no different except for the fact that he doesn't possess the adequate social grace to know that staring is rude. Just like his wildly inappropriate comments, which may or may not be delivered with impeccable timing. It doesn't matter that they're actually sort of funny or that it's mildly endearing to see a grown man laugh unabashedly at his own stupid jokes. They're still rude. Even his smile afterward is imperfect, crooked, just a little cocksure. He's too tall, also. And pallid. Does the man never undress to feel the sun on that pale expanse of skin? Maybe he only undresses at night. In the weak light that filters into Darktown.
The point is that Fenris isn't bothered at all by the mage staring at him. He's also not bothered that more and more often, he has to stare right back. After all, mages must be watched very, very closely.