Symbolism, Imagery, Allegory
Did you know that it's illegal for men to appear without a shirt in Tonga? Or that in the cities of Wildwood and Penns Grove, New Jersey you could get fined from $25 to $200 for wearing baggy pants? So what does that say about Willie? He spends most of the play wearing close to nil, and then, suddenly, he's wearing a tuxedo.
Willie's outfit is described as "dressed to kill." That sounds a bit ominous, doesn't it? His outfit is something you'd wear to a wedding… but it's also what you'd wear to a funeral. The confusion we feel toward the way Willie's dressed also adds to the general sense of confusion we get at the end of the second act. But how would the audience know whether he is dressed to actually kill Winnie? It's not stated in the dialogue that he's "dressed to kill," but rather written in the stage directions. Could Beckett be offering a sign to those who read the play?