Let's say that there's some really amazingly sexy guy you work with occasionally at your job. You always seem to be bumping into each other, or having other slightly awkward moments. One day you seem him in the lunchroom alone, looking absolutely wrecked. He complains about the dark circles under his eyes, and you nonchalantly say "I didn't notice." There's a slight pause before he says "Thanks!" with an unusual amount of enthusiasm.
Here's the question: Would that be accidental flirting? Was that the wrong thing to say?