What are some not illegal, but morally wrong tactics you use?

I’ll admit, in very specific cases I’ll start hitting winners in warm up. If I am playing someone who is ranked a little bit higher than me, and comes with the attitude that they think the match will be light, I’ll usually rip 3-4 drives as hard as I can without making it look like I’m trying, then say I’m warm and block for them. It messes with those players to not be able to put seemingly mid power shots back on the table.