Some phrases that confuse me

There are some things that people say, that my immediate interpretation of the phrase is strongly opposed to the intended meaning, which causes a strange discord in my brain.   It's like, I'm following the emotional sense of what their saying and then they say something that produces an emotional sense that is completely out of place, and I have to go back and look at it again to work out what it's really supposed to mean.

A trivial example is the use of "fight with" to mean "fight for" or "fight on the same side as".   I am very much socialised with the use of "fight with" to mean "fight against", for example, "I got into a fight with a boy at school today", "We're having a big fight with the council over their plans to close a local school" and so on.   Context usually gives me enough to work out whether "fight with" means "for us" or "against us", but when it's "for", I have to take a few moments longer to figure out the sense of the statement.

This post was really motivated by a phrase that until now I had only heard in one place, but it came up again recently with this:

Before this, I had only heard it in the lyrics of Coldplay's song "Fix You" (a song that annoys me quite a lot, but that's another post entirely).   In both contexts, it obviously is meant to mean something good (although Google has not yet been much help in working out what good thing it is supposed to mean, exactly).

But to me it means something bad - the image that it conjures in my head is of bones literally bursting into flame, of burning, and pain, and crippling devastation of the body.   I cannot shake that horrific image, and the meaning that i would expect the phrase to have would be along the lines of "My arthritis gets so bad sometimes, it feels like it ignites my bones" - for a literal expression of being in a lot of pain.   I would think to use it also of an emotional situation where a person feels extremely hurt and hamstrung by what someone else has said or done.   Like the phrase "it burns me up inside when you do that" but coupled with the specific thing of the cause of the pain also making it impossible to manoeuvre or escape it.

That one really does require a mental screeching of brakes to go back and reinterpret the emotional content of a person's speech.

The other one that I have had on my brain lately is "fill your boots", which is really something like "Make free with it!", "Make hay while the sun shines!" "Help yourself!" etc.

The image that it conjures for me is one of fear, akin to "fill your pants" meaning to crap oneself with fear, although the image that it produces for me is not excrement but urine: what "fill your boots!" produces is the idea of piss running down a person's leg into their footwear, again, as related to the physiological reaction to extreme fear.

(It turns out that there are some uses that do mean what I thought it to mean, but I have never heard it used in that context, only in the sense of "help yourself" etc.)

The example given at Urban Dictionary of: "Are those sweets free?" "Fill your boots!" gives some idea of the dissonance that this can produce: "Are those sweets free?" "Be so afraid you piss yourself!" reveals the sort of mental reinterpretation I have to do to fill in the blanks with what it's supposed to mean instead of what I take it to mean.

The frustrating thing with all of these is that even though I a now aware of what the phrases really mean (or mean most often), I still have my initial "instinctive" interpretation first, and then have to go back and write over that with what I know intellectually is supposed to go there.

One other point occurs to me.   On all three examples mentioned here, my interpretation produces a negative emotional response when a positive emotional response is intended.   What (if anything) does that say about my worldview!?