My co-worker just told me this one today (I hope it's not offensive!!!)
Q:How many ADD kids does it take to change a lightbulb???
A:You wanna go for a bike ride??
My son has ADD, yet that so isn't offensive! I think it is hilarious because it is so true!

My radio station that I listen to has "Worse Joke Wednesdays". The worse joke wins a prize. I can't remember any off the top of my head right now.