Actually, I have a few more... it's not so much advice as just stupid things clients or their employees have said.
There was this one bank I did work for in 2017 that was nothing but headaches, but the two biggest headaches was their IT director, and VP of marketing.
"you can't make a site responsive without bootstrap, it's what makes sites responsive" -- their head IT guy was 100% convinced that was the truth, when -- as always -- this guy knew not one blasted thing about HTML or CSS, and didn't even know what a media query was. He even started to try and convince the president of said bank that I didn't know what I was talking about -- which is when I snapped, and said "look, I wouldn't even be here if this {expletive omitted} had any {expletive omitted} clue what he was doing. You hired me to fix the mess this {expletive omitted} made, and the only thing I'm trying to figure out right now is why the {expletive omitted} you haven't fired this {expletive omitted}"
I did so in command voice too. For those of you unfamiliar with command voice, go watch "Boys in Company C" and "Full Metal Jacket".
Their marketing director was no better -- they threw a conniption fit when I yanked all the bloated slow goofy flash animations and scripting heavy BS off of the banking portal -- you know, the part where people go to do things like check their balances and make transfers. Their reasoning "It has to be flashy and fancy to draw in new customers"
On the banking portal... aka behind the client login... aka something people who didn't have accounts with them yet would never even see.
Of course this was the client where I got them out of their legal problems, left them with a nice clean fast usable accessible page that met all WCAG requirements to get them out of their continuing fines... and not two weeks after we get them clear of all the legal woes those same two {expletives omitted} went in and put everything back exactly like it was -- then were shocked when sued again, and tried to blame me for it. I went from "guy hired to fix it" to "witness for the prosecution" -- as it went from "they didn't know any better" to "willful and malicious".
Somehow those same two {expletives omitted} are still with that bank, but hey at least I got paid triple by the time the legal hell was settled.
There's a reason I've started to think that modern marketing executives and many IT "suits" are just burger flippers with degrees. Actually, that's insulting to burger flippers; even they'd probably know better.