The Midrash Shmuel on Avot 3:7 says that the Tanna of the Mishna has Iyov 30:4 in mind, where the Targum says the verse is referring to someone who interrupts their learning to engage in worldly activities causes destruction to his food. The Tanna did not include the verse because this was common knowledge:
"Nachas" is a Yiddish word/concept that signifies pride in someone else's accomplishments, usually those of one's children. So by extension, "nachas rights" signifies the right of a parent to brag about such accomplishments.
Five conditions of a hiddur esrog according to the Tiferes Yisrael Sukkah 3:37 from most to least important.
That it should be completely clean,and especially by the chotem (when the middle starts to bend in) there shouldn't even be pin drop of something unclean.
The esrog should have many bumps and not be smooth skinned.
The ukatz (bottom stem of esrog) ...