quaint

In this sentence, the speaker refers to war as "quaint," which means "having an old-fashioned attractiveness or charm." i don't think he says this to be taken seriously, but rather in to be taken in a sarcastic tone. This is due to the fact that, the rest of the poem seems to say that the speaker does not really think war is "quaint." He seems to regret the murder and says that, if he had met the other man in a bar, he would have bought him a drink, not killed him. So I think the word "quaint" is used instead to actually complimenting war he is more insulting it and saying it is so bad that you can't you it is good and people will immediately know you are joking. It is sad that he says this because you know in saying it he is again feeling the regret of his action