Nobody says that's ALL you have to do. How are you taking this personally? How do you think the tip is secretly meant as an insult? I can see that if you've thought about this a lot and tried many things, it could be frustrating to see simple tips like this. Regardless, you're reading more into people's personalities and their intentions than is really there.

What this means to me when I read it- many people have a very sensitive sense of smell and after even any light activity or enough time, people will not smell perfectly clean anymore. I have showered and then spent 15 minutes working on something and then been told that I smell. Good luck if you meet someone that has a sensitive sense of smell- you will probably be told to take a shower whenever you are not perfectly clean and want some physical interaction. Will you tell them "that is secretly meant as an insult against people like me who have tried everything...." Or will you take a shower? Then you'll be told to shower every time it's relevant, maybe multiple times per week, that's on top of showering every day. Now you've been informed that there are people like this. Relationships require some accomodation to the other person's wants, and hope the other person will likewise make a similar effort to accommodate the things that are important to you.