For the record (for whatever that is worth here): I have
heard every single utterance that I mentioned in #4 and I also realise that not everything in #4 will be directly relevant to the query in #0. I did
begin with the preamble of "Probably not quite what you're looking for, but perhaps interesting to you nonetheless
" to make sure everybody knows that the things I mention in #4 are only loosely
related to the query on a conceptual level.
I agree that having a source to back up a claim will always be preferable to just stating something and asking others to give me the benefit of the doubt. But with these types of colloquial utterances I find it difficult to back up my claims, so let me at least backpeddle somewhat and say: Not every colloquial utterance will be so widely known that everybody is familiar with them, some colloquial utterances are born on the internet and do not make the transition into colloquial speech, and dictionaries are often slow on the uptake of colloquial utterances (as they should be, since a lot of fads are over as soon as they've begun).
I would just like to apologise for mentioning colloquial usages that I cannot back up with a source (besides the weak claim that I've heard the things I listed and did not create or fabricate them) and also, more generally, to advise non-native speakers to be careful with colloquial utternaces. If in doubt use something that is in a modern dictionary or adopt the utternaces and phrases of your peers and by appropriately wary if you decide to introduce new-fangled words, terms or phrases into your group.
I should have mentioned that I know "To take something with a pinch of salt" with two meanings, depending on context. But let's agree to disagree on "the pinch of salt" with the meaning I explained in #4. I can only reiterate that I have heard it used to mean "don't take what XY said to heart/don't sulk", but if so many others disagree, then forum users should avoid using it in the way that I mentioned.
"Don't be so salty" (and creative variants like "that guy is one salty saltine") in colloquial usage in more than one instance, uttered by unrelated people. For context: It is something that will often be heard in the context of competitive multiplayer video games, mostly by people around the age of 20-30 (if I may take an eduacated guess). Said to people who are sore losers or people who "ragequit".
"To be butthurt" is fairly well known on the internet, you should even be able to find a "butthurt form" to print and fill out along with many instances of usage.
(On a personal note: I also do not find the concept that funny, but "the internet" generally behaves like a 12 year old, so it should not be that surprising that this particular phrase has become fairly widespread.
I think everybody using this forum should be able to discern all by themselves whether they want to incorporate this type of lingo into their daily lives.)
I've also never heard or seen any utternace of "sorehead" before. But that only means I haven't heard it before, that doesn't mean I would advise against using it.
I think with any colloquial utterance, you have to be prepared that somebody might not understand what you are going on about.