The only thing that is bush league is complaining about a perfectly legal shot and the only unwritten rule is that there are no such thing as unwritten rules. And if you are willing to let non-existent unwritten rules remove a weapon in your arsenal that may help you win a match, then you are no competitor. As Billy Hoyle said in White Men Can't Jump, you'd rather look good and lose than look bad and win.
I've used them before. I have a decent first serve and when someone starts sitting 7-8 feet back of the baseline, I have no problem dinking one over to let them know that it could come at anytime. Just the fact that the possibility is there makes the 1st serve more effective. I've gotten plenty of giggles and raised eyebrows with it.
And if I'm playing someone who isn't mobile or is gassed, I have no shame in drop shotting them to death. What are you supposed to do, sit there and hit it back and forth until someone misses? If you perceive a weakness, attack it. If someone has a strong net game, loves to approach, and is in shape, then you find another chink on the armor.
I do understand, especially in this day of nothing but pure power, gorilla tennis, that some people see strategy and specialty shots as so-called bush league, but to me, this is the greatest thing about tennis, the chess match, the tactical element of the game. Just one hackers opinion.