A belated comment as I've been away. Ihor seems spot-on with his explanations. But I think it is "nitties" not "knitties" - I picked up this from somewhere:
"Box back nitties are those long flannel underwear with the flap in the back for, well, you know :) For an example, see Michael Landon in Little House On The Prairie." There was a also a quote from Garcia (originally I think in the 1993 Golden Road annual): "I have no idea where he [Pigpen] picked up most of that stuff. Some of it was bits and pieces of lyrics from old tunes that he'd pick up and then he'd extrapolate. But, like, I have no idea where he got that thing he used to sing [during "Lovelight"]:'She got box back nitties and great big noble thighs, working undercover with a boar hog's eye.' Don't ask me--I don't know what the fuck that's all about! It's some weird mojo shit or something. But he could always pull that stuff out.He could do that as long as I knew him. When he was on, he was amazing." Alex Allan
