This is The Cat's Mother definition of stereotype.
Stereotype: To lump everyone in the same basket.
To say that everyone in Texas is a bible-wielding-gun-holding-crazy-guy.
That isn't true.
We know someone from there, and she doesn't act like that.
Of course she could be the only one and thats why she can't make any friends :)
But that's still not everyone.
Note: The Cat's Mothers words.
If this didn't help here is the definition from http://dictionary.reference.com
–verb (used with object)
to make a stereotype of.
to characterize or regard as a stereotype: The actor has been stereotyped as a villain.
to give a fixed form to.