thoughts on stereotypes

Why are stereotypes considered a bad thing?  I think when used appropriately, they can actually be an advantage.  For instance, blondes are considered dumb.  Because of my blond hair, those I work with think that I, too, am not the brightest.  Little do they know that I graduated college Summa Cum Laud with a grade point average of 3.949.  This actually gets me out of having to do a lot of crap that I'd rather not deal with.  Example number two: the middle child syndrome.  Because I am a middle child, I  have an automatic pass on some of my stranger quirks.  I just shrug my shoulders and say "middle child", and people seem quite satisfied with that answer.  What is really disappointing is when certain stereotypes turn out to be less than truthful.  As I have gained weight over the last few years, my disposition has, in fact, become more jolly.  So when I meet an overweight person who is not funny or fun to be around, I get the same feeling I got when my mom told me that Santa did not exist.  Case in point: I know a person who by all accounts and stereotypes should act in a certain way. And for awhile this person did. Suddenly, she's breaking the rules of her particular stereotype. I don't think I like it.  Was it all a ruse?  All I am saying is that perhaps, there is a reason for stereotypes.  And if you fall under the category of one, would it kill you to play along?  I like my fat people jolly, my old men grumpy, and my bosses clueless as to what really goes on in the company.