Good points, thank you.
Someone in the past I played a match against once would open their mouth like an O when they were serving. Like they were yawning. It was very off-putting (but not illegal). Was really distracting.
My personal view about people who take their time with the serve is it's bad manners. When they stand still for 20-30 seconds a serve. But like you said it's not illegal, and in the above situation it's a good thing to try.
Yh, I like to focus on my own game; make myself play better instead of trying to make everyone else play worse with antics that distract from the badminton. It's only a tool to combat players that jump the serve. If the opponent is receiving legally, why would I distract myself with psychological games.