It's true, being attractive is generally the least of Cade's concerns, though he does at least try to present himself well for the most part. He almost protests when Zevran continues, but bites his tongue; the emotions bubbling up inside him are the sort that make him say and do stupid things, and he has no room left for those.
He does, however, crack a bit when Zevran implies he might want more out of it than punishment. "I don't," he snaps, but his demeanor is more desperate than angry. Perhaps it's better to call this off now, before it can get out of hand. Before he can be any further corrupted.
He regrets thinking this as soon as Zevran offers him the potion-- Zevran, the person who has been helping him-- or has he? Maybe this is just some sick stunt. Maybe he was sent by the Dalish.

Cade accepts the flask, but only long enough to take one sip that might be the duration of two. Then he hands it back, quite forcefully, and gets to his feet with a hiss. Oh right, that. Hastily bailing out will be hindered a bit by the fact that putting his shirt back on will be slow murder.