Are there any expressions to describe being compliant in particular occasions? [closed]

I know that for a person who normally avoids confrontation, in English we have several expressions such as jellyfish, pushover, soft touch ....

But these expressions are too general for my purposes, describing such a person's usual character trait. So what are words or expressions – if any exist – we could use for someone finding themselves a soft touch in a particular instance? In addition, are there words or expressions for putting another person in such a situation?

Solution 1:

For a single lapse, there's the very common expression [have / show] a moment of weakness:

a moment of weakness – a short time during which someone makes a bad decision or does something bad that they would not normally do

• He kept asking me to help him, and in a moment of weakness I said yes.

[Cambridge Dictionary]

Though it's a hypernym, it's very often used when someone complies tamely when they should say no. It's also often obvious humerous semi-hyperbole, as in the following example:

Since I started working with Dan Clarke, he’s been nagging me to do one his .NET Oxford talks on the subject .... Anyone who knows Dan will know that he doesn’t take no for an answer – so in a moment of weakness, I agreed to do it....

[Dave England_.Net Oxford]