For what it is, the Circa '21 Dinner Playhouse's Nana's Naughty Knickers is rather amusing and somewhat unexpected. The title, for me, conjures up images of scantily clad grannies telling off-color, elderly-themed jokes in a wild farce. Instead, playwright Katherine DiSavino's piece is a mild farce, with a unique plot and interesting, likable characters (and only a handful of age-based jokes). I didn't laugh quite as much as I expected to during Friday's opening-night performance, but I was more engaged than I anticipated I would be, and interested in where DiSavino would take her characters.