I checked a few other translations on this apparent lapse in charity. They pretty much say the same thing, and/or commentators footnotes say that this is what is meant by the alternative verb, "mutiliate."
Now, it's true that we don't have all the context, cultural standards of the time, nor the tone or expression Paul had in mind when he wrote this little bon mot. Perhaps if we had all that, we'd know it was just a gentle, poking of fun at the Judaizers. Or maybe there's commentary from St. Augustine out there explaining how Paul was really justified in what he said, and I'm just too ignorant to see it. But assuming that this is what it appears to be --Paul not being very nice- what can we learn here?
1.Until we're dead, holiness is a work in progress. Even in really, really holy people like St. Paul
2. We should not get discouraged by our lapses, by always having to say the exact same thing in confession, etc. If it happened to Paul --who had actually come a long way, since before his conversion, he would kill his enemies, rather than make sarcastic remarks about them--it can and will happen to all of us.
3. Oops! Its 11 in the morning and I didn't say Morning prayer yet. If you have any reflections to add on Paul's snarkiness, feel free. I gotta go.