P.E. is the height of embarrassment for anyone who is not athletic. I hope things get better for your son. When I was going to school, there were some real bullies who made P.E. a miserable experience for me.
That's exactly what I went through too, plus having some PE teachers who were quite mean! Things got slightly better in junior high, when the boys and girls were separated for gym class.
I'm with Nannarob earlier - "NEVER EVER GIVE UP." I believe we can beat this AS tendency thing, get out from under the rock, and I believe I have - see website below. Very, very best