Let's take a totally hypothetical situation as an example. Pretend you own a commercial cleaning business, and your wife has sacrificially given up her time (that she could be spending writing) to work for you three days a week. It's the day after Christmas, and you both are walking out of an attorney's office (that you've just cleaned). Oh, and you've parked your black Ford Explorer in a different spot than normal.
(Note that you have only had the Ford Explorer for a couple of months, and your wife is not used to knowing the subtle differences between your Explorer and every other black SUV on the planet--mainly because she doesn't care.)
You pass a black GMC SUV parked in the same spot you usually park in. You walk past this black SUV on the driver's side. Now here is the important part. Your wife isn't fully paying attention because cleaning toilets and office buildings bores her to tears, and to survive such mentally unstimulating tasks, she resorts to thinking about such things as how she is going to get more book signings or how she is going to end her third novel. (Totally hypotheticalsituation here.) So your wife, still thinking about her marketing plan and budget, walks up to the passenger's side of the black SUV--parked in the spot you usually park in--and starts to open the door...
...until she notices some one sitting in the passenger side of the SUV and quickly walks away as though nothing had happened to hide her embarrassment.
Should said hypothetical situation occur, you should be very careful not to tell you wife that she is dingy and then compare her to a dumb blonde. Should you be so careless, AT LEAST don't continue to tell her she is dingy, even after she shows signs of hurt and annoyance.
The reason you should refrain from such behavior has nothing to do with hurting your wife's feelings, furthering her embarrassment, or reminding her of her horrible middle school days when she was a total dweeb. See, here's the thing: if your wife is between the ages of 30 and 35, there is a big chance she might have been a huge fan of the New Kids on the Block when she was in middle school. And if your wife loves to sing, there is also a big chance she might have memorized every single song the New Kids on the Block sang, simply because she would have only had cassette tapes to listen to way back then, hence having to listen to every song because she couldn't hit "skip."
So, why should you never tell your wife she is dingy? Because if you will be stuck with her in a car for a while, she might decide getting even might be more fun than getting mad--especially if you are unaware that she ever listened to such music because her tastes in music matured when she entered high school (well before she met you). The fact is, you might be blissfully unaware of your imminent danger.
Your wife, calculating the length of the car ride, might dream up a scheme to get back at you that only a few brave souls might dare attempt. She might serenade you with oh, oh, oh-oh, oh tons of New Kids on the Block songs that she hasn't even listened to in over 15 years--just to annoy the crap out of you. (Ah, yes, one of the problems with marrying a woman with a great memory.)
If this happens, you had better show your wife that you've got the Right Stuff by Hanging Tough and earning her forgiveness Step By Step. Otherwise, you might be saying, "Please Don't Go, Girl!"