(continued)
One sort-of street term for this is:
"OK, don't try to Slime Out of it".
Which refers to attempting to wiggle out, when proved wrong, in arguments.
Often, at least in my experience, the other party is a family member, job boss, or other untouchable figure, and so we tend to just shrug and give them a break...the out that they seek.
But, in some settings there is the option of 'pre-empting' some person that has done this wiggle-out. I've used THAT verbal self-defense method, saying something like:
"We discussed that, yesterday, and you kept changing the subject...".
Response comes, (still unacceptable), that they 'stayed on-topic', but you maybe just have to insist:
"No, ....it's a waste of time, to debate when you respond like a small child. Come back when you are willing to stick to the original issue...".
Relatives do the 'topic shift', in what I learned to call a 'Drive-by'. That's a label borrowed from gang warfare, but verbally a relative would fire off some typically political smear / insult, but then suddenly retreat into territory of 'polite' where you (feel) obligated to drop any possible defensive response. That's why I call that a 'Drive-by', as the setting is suddenly in territory of being civil.
Very frustrating, when it's a relative, commenting about an overweight issue, for example!