sponge what?

Just a quick story here- we stopped by Dollar General aka the dollar store to pick up a few cheap
supplies. While there I noticed some marked down DVD's- including a Sponge Bob DVD. Yay. I picked that up, along with the other stuff, and when the cashier was ringing things up, was surprised to find out (actually all 3 of us were!) that something we were buying required age verification???! HAHA? What could it be? Here is what we got: tape, light bulbs,
batteries & SB. Have people found a way to make drugs out of batteries? Is it some bootleg SB
that really isn't cartoons? Has SB actually been found to promote obscene amounts of silliness
and random goofy behavior?
These are things that I would like to know... perhaps they have an age check for any DVD's, in case they are Rated-R? I buy DVD's so infrequently, I really have no idea if that is the case.