They* always jumped all over us for using a double negative when we said "I can't hardly ..." in my youth. I could never see that hardly was a negative. When you say "I can hardly ..." you're saying that you can but it is with extreme difficulty. If you look at "I can't hardly ..." logically, then it would seem to mean that you can do it easily but, that's assuming that language acts logically, an extremely iffy proposition.

*You know darn well who they is so don't be asking. It was the same they that got on our case for saying "Can I ...?" when we were asking permission even though they used "Can I ...?" theirownselves.