The Handbook is for optimal dress guidelines. Nice jeans are fine--torn, dirty anything is not acceptable. No sleepwear/curlers/swimwear, muddy boots, nasty slogan Ts. They want nonrevs to look inconspicuous--wearing a sport coat and tie to Cancun screams "nonrev". Behavior is more important--changing seats, complaining about anything like meals, delays, etc can jeopardize your employee's privs. DL has a whole series of videos and some of them are really humorous/OTT but I've seen some odd behavior from NRs.
Just use common sense and you'll be fine!