In the spirit of that, but with a new spin, what would you NEVER do in game? There are various exploits that get you more money, help you win games, etc, or you can take over your rivals and destroy them, or maybe you free transfer your favourite players the day before you take a new job...
Yes I have done all of those
Mine is that I never use tactics built by someone else. If I designed the perfect wib wob that swept all before me then you're damn right I'd use it every game, but using someone else's tactics feels wrong to me, it's essential to my sense of achievement that I designed the tactics and player instructions. What is the line you guys never cross (or maybe crossed once and said I'm never doing that again)?