What is the most unhelpful advice you have received?
I'll go first: "You have to have children when you're young," told to me when I was in my late 20s, with no desire to ever have kids, and no means to support them, by someone divorced multiple times with at least one adult child who does not speak to them.
Also: Responding to "How do I deal with this problem?" questions with "Oh, don't worry about it, it's enough that you're even thinking about it!"
Idk man, I've never gotten married and it's been fine for me. My girlfriend and I have been together for 14 years, have 2 kids, and our family is all that has kept me going through this shitty world. Never married though, so many there is some truth to the advice.