HISSSS-TERICAL! Now, about the shell...
I gotta admit, it's just SO annoying when that happens to me! However, I heard there's a way to avoid the Blue Shell in MK:DD, MKDS and MKWii: you just gotta have at least one Mushroom with you, and then use it right when the Blue Shell aims down to hit you (precise timing is needed, so that's why I didn't manage to do it up to now...)! It's best if you get a Triple Mushroom, use the first 2 normally, and save the last one in case of emergency. After all...
Better be safe than sorry, right?