The following is an excerpt from my book, Cats in Charge: A Guide to the Training and Education of Humans. It's available at Amazon.
If your humans think that a photo of you is worth Facebook exposure, it MAY means they hold you in high esteem. You always want to encourage esteem, which, if correctly encouraged, may lead to an appropriate attitude of worship.
However, if they post a photo that makes you look undignified (dare I say, ridiculous?), you need to reconsider not only the value of exposure but the degree to which your human holds you in esteem. Serious corrective action may be required. (See my book for details.)
If your humans put you in an outfit and start rolling on the floor, helpless with laughter, you can safely consider yourself humiliated. Remove and shred the costume.
If, instead, they're only smiling and saying things like, "That's so cute; we should take a picture and put it on Facebook," consider allowing them their childish behavior and demand many treats in payment.
If the outfit in any way inhibits your freedom of motion, decline to model it. This is especially important if you live in a household with small children and/or dogs. You must always be ready to flee at any moment.
If it's Hallowe'en (and you'll know because the house suddenly becomes filled with totally inedible food like candy corn, popcorn, apples, and other such nonsense), you might consider giving in because this is a day when humans also wear ridiculous costumes.
If they want to put a crown or tiara on your head, graciously concede and look extremely regal.
I have seen photos of cats sitting at tables with napkins around their necks. While the napkins are generally unnecessary, humans should be encouraged to welcome cats to their tables. This seating plan gives cats easy access to human food.
In summary, the clothing question must be taken up case by case. Once the photo is posted, be sure to read the comments. If any of them seem to be making fun of you, think twice before allowing your humans to photograph you wearing a Miss Piggy hat or an oversized woolen cap with a pompom.
Be especially cautious if they want to put you in a tutu or prom dress and high heels. If Barbie Cat were unexplored territory, I'd encourage you to go for it. However, it's been done, and the only thing worse than public humiliation is public humiliation plus coming late to a trend.
It would be unfair to end this without the principle of "different hats for different cats." Some cats enjoy wearing human-style clothing.
Feline behaviorists have attempted to float a number of developmental theories to explain this. Drag cats have no patience for such hot air. In their words: "It's my thing. Get over it."
If clothes are your thing, don't let your owners dress you in cheap fabrics with poorly stitched seams and dragging hemlines. As with food, toys, treats, and general accomodations, follow the Tara Principle.
Insist on the best. Always.
To buy this book, please go to Amazon.