If someone gives you a roguish smile, he’s totally flirting with you.
You can't trust someone who acts roguish in the bad way, like the roguish crook who picks your pocket while telling you how lovely you look. On the other hand, you might like someone who acts roguish in the second sense, which means playfully mischievous. Being roguish in this way might mean playing pranks, telling racy jokes, and being a little wild. Roguish behavior like this can still be annoying, like if your roguish roommate at camp short-sheets your bed."