Rod Stewart obviously spends a lot of time thinking about sexiness -- after all, he is the guy who famously posed the musical question, 'Do Ya Think I'm Sexy?'

As Stewart told 'Piers Morgan Tonight' (Weeknights, 9PM ET on CNN), his charmed rock star lifestyle has helped him develop a pretty specific idea about what makes a woman sexy.

"I've been out with women who've been 'Playboy' center-spreads. Absolutely gorgeous features, but no sex appeal," Stewart explained.

"What to you is sexy?" Morgan wondered.

"It's an inner thing, it's a look in the eye, it's almost a slight -- get me right here -- a slight sluttiness. Just a touch of it."

"Just a skirt a little bit too shorter than it should be. A glimpse of stocking, maybe," was how Stewart defined "a slight sluttiness" when Morgan asked.