Tuffy, my Maltese, shuts down whenever I put clothes on him. I sometimes do it to calm him down and get him to behave because he is super hyperactive. My guess is that they just aren't accustomed to it so they just act weird.. or maybe it's because they are boys.. *lol* but look on the bright side, he'll be super easy to take pictures of! My Yorkie Pixie seems to love clothes.. I guess it must be the girl in her!
