How many times have you dropped your iphone 4 without case?

That wont hurt it, I dropped mine (5S) about 4 feet onto tile floor, no issues. I dont think you would have any problems unless you dropped it on cement or dropped in water or dropped it so the screen hit down on a a hard surface. (Mine is aluminum case, but I also dropped it on cement once and have no problem, but I hold it tight in my hand now :)

I accidentally threw mine across the class room and works fine

Once.