You know you're perverted when ... you automatically begin or end a comment with something along the lines of "keep your mind of the gutter". Because, you know, you said it anyway and your mind was totally already there.
When @sprinkles says "thinking suitcase", and you immediately picture a suitcase with a face, licking its lips, beckoning towards you with one finger, and winking. Also, the suitcase is full of sex toys.
When that one time you accidentally stare at a woman's breasts, realize the social implications were not nearly as bad as you had expected even though she had little to no interest in you, and then begin planning social experiments for how you could do something similar to other women upon them giving consent. All theory, of course.
You know you're perverted when the above post makes you picture Emma Watson slowly putting her lips around an ice cream cone, with her lips curled a sly little grin and eyes beckoning me to come hither.