Oh far, far too often.
Actually that is my reaction to being 'put on the spot'. For example, when I was in school (nursing school, dropped out because of the SA) I dreaded everyday because I had this math teacher who KNEW how hard it was for me to speak in class, he knew how i reacted, AND he knew I was just plain terrible at math, which made it all worse.
He used to purposely ask me a question, knowing that I can't even speak when everyone is looking at me like that, and then he would keep bugging me to talk, and then make some comment like "oh, maybe she will answer us later".
I would get so worked up during this time I would have my head down, trying to hide my face with my hair because I would be crying like a child.
Embarrassing and yet, I can't help it. Worst part? I was 27 years old at the time.
/sigh
And that happened at least 3x a week in any given class, but his was the worst, my other teachers stopped bugging me after awhile.