Let's not forget that it's also the symbol for modulo operation. So many opportunities for ambiguity!

The difference between you and the people this meme is about is you understand that both space or no space are fine.

For more context, I was trained to use a space between a number and its unit (e.g. 2 mol, 3 g, 1 M) for scientific writing. This includes the % sign when it follows a number (i.e. 100 %). So percent yields would be reported as 78 % instead of 78%. On the flip side, units that contain the % sign would not use a space. For example, mol% and wt% would not use a space to separate the % sign from the rest of the unit (i.e. 2 mol%).

Since I was taught this from the very beginning of university, I never really questioned where the convention came from. Now, I work for a PI who does not use the space for %. Every time I write something (presentations, manuscripts, etc.), they clarify that % is a mathematical operator so there is no space. After a search to defend my position, I found the SI brochure from the Bureau International des Poids et Mesures that clearly states the use of a space.

Recently in group meeting, while talking about something kind of related to units, they said that I believe there should be a space for %. I quickly clarified (and showed the SI brochure as evidence) that I do not "believe" there should be a space; this isn't something I have created in my mind. Finally, they said that since it is their lab any manuscripts must follow their convention. Now when I write, I write my way and change it when I self edit before sending it to my PI.

Square root is an operator that maps a number to the positive number that when squared returns the original number

Nah, dog. You're arbitrarily ignoring negatives. The square root of 4 is ±2.

Nah, dog. I'm wrong