Ramban and Rashi say that Naval means an ingrate who isn’t: כ ְּמ ְּירְּ טוֹהב ְּ grateful. The Yetzer Hara distracts you into focusing on other people’s accomplishments, to subtly make you be M’vazeh your own.
Ramban and Kli Yakar compare the word “Naval” to Naval the husband of Avigayil. They mention that there are two opposite types of people; a “Nadav” who gives others even without being asked, and a “Naval” who doesn’t appreciate.
Dovid had done tremendous favors for Naval. Afterwards, Dovid asked him for some food for his men, since it was Rosh Hashanah. Instead of appreciating and showing gratitude, Naval was M'vazeh Dovid. Dovid vowed to wipe out Naval (and his followers) by the next morning. But Avigayil came running, and told Dovid that he wasn’t really a Melech yet, so he doesn’t have the right to kill him.
She was a Nevi'a, and she said: “Let Hashem kill Naval”; and that night Naval had a stroke, Rachmana Litzlan. He had Aseres Y'mei Teshuva to do Teshuva, and he didn’t; so he died on Yom Kippur. She also hinted to Dovid that she’d like to be married to Dovid as soon as Naval dies. The Meforshim ask why Dovid didn’t get so angry when Shim'i ben Gera was M'vazeh him, and he let him live.
