Meaning of four words

The passage below is from A History of the Index by Dennis Duncan.

Buckley’s hardline conservatism, however, began to exert an influence on the election, drawing the vote rightwards, something which ultimately worked in Lindsay’s favour. Meanwhile, Buckley’s oratory – lofty but witty, a blend that before long, and for the rest of the century, would see him installed as host of the Firing Line current affairs show – caught the popular imagination. Though polling only 14 per cent of the vote, he had played a galvanizing role in the election, and delivered some of its best lines, including his famous, off-the-cuff answer to the question of what he would do if he won: ‘Demand a recount.’ In the wake of this public attention, then, it was little surprise that Buckley should spend the next winter following the tried-and-tested path for politicians with time on their hands after an election defeat: he wrote a book about it.

Buckley’s The Unmaking of a Mayor arrived the following October. One of its minor spats – among many major ones – is played out in a footnote and concerns Buckley’s friend and rival as a public intellectual Norman Mailer. (It was, in Mailer’s words, ‘a difficult friendship’.) Buckley accuses Mailer of refusing to allow him to quote from their correspondence in his book, ‘perhaps because he regrets a pleasantry directed towards myself’, a jibe that speaks as much about their friendship as their enmity. Given that the pair had disagreed about whether their private communications should be made public in Buckley’s book, it was only appropriate that Mailer should be the recipient of a complimentary copy when it came out. At the back, on page 339, beside the index entry – ‘Mailer, Norman, 259, 320’ –Buckley had scribbled a personal message in red ballpoint: ‘Hi!’.

In this passage I’m not sure about the meaning of the underlined words.

First, ‘unmake’. In context of ‘The Unmaking of a Mayor’ the word seems to say ‘failure’, because he failed to be a Mayor of New York. But dictionary says a bit different things as follows:

https://www.thefreedictionary.com/unmake

1. to undo or destroy 2. to depose from office, rank, or authority

I think #2 meaning fits to the context but it doesn’t fit quite well with my conjecture. Can you tell me what I have missed?

Second, ‘concern’. I think it means ‘is about’ in this context. I’m pretty sure about the meaning I suggest, but I want my meaning to be confirmed.

Third, ‘pleasantry’.

https://www.thefreedictionary.com/pleasantry

1. good-humored teasing; banter. 2. a humorous action or remark. 3. a courteous remark used to facilitate a conversation.

I think the word in the context seems to fit the meaning #1. (Am I right?)

Last, ‘jibe’.

https://www.thefreedictionary.com/jibe

jeer, sneer

‘Jibe’ seems to refer to ‘perhaps because he regrets a pleasantry directed towards myself’ in the passage. (Am I right?)

And it seems to mean ‘jeer, sneer’. (Am I right?)

Still, I am a bit suspicious about a jibe, a sneer can be ‘speaks as much about their friendship as their enmity’. Does it hints that their relationship was one of love and hatred?

Thanks in advance.