What does the Pasuk mean when it writes "Bocheh le'Mishpechosav"?
Rashi: It means that, when they gathered to complain about the Manna, they did so in family groups in order to publicize their complaints.
Rashi (citing the Sifri): It means that they now began to grumble about the prohibition of incest. 1
See Sifsei Chachamim.
QUESTIONS ON RASHI
Rashi writes that they cried about Arayos. Why did they cry only now - they should have cried at the time of Matan Torah?
Riva: They did not want to mar the Simchah [of Matan Torah].
Lev Eliyahu (Sh'mos p.101): Mi'd'Oraisa they were permitted, since they were like Geirim. However, in some cases, the Chachamim now issued a decree forbidding a Ger to marry his former relatives.
Oznayim la'Torah #1 (on Pasuk 4): It is only after they began crying about the lack of meat that they went from one sin to another and began crying sbout forbidden relations 1 - since 'Aveirah Goreres Aveirah' (One sin leads to another).
Oznayim la'Torah # 2: Because as long as they were standing in front of Har Sinai they were overawedbv by the samctity of the location and accepted whatever Moshe told them willingly.
Oznayim la'Torah: As hinted in the double Lashon "His'avu Ta'avah" - in Pasuk 4.
Rashi writes that they cried about Arayos. Surely many had married relatives, like Amram, and now they needed to divorce and break up the family. It is proper to cry over this! Why was Hashem angry? Why does the Sifri call them Resha'im?
Lev Eliyahu (Sh'mos p.101,2, 105): Everyone is judged according to his ability. They lived through the Makos, Keri'as Yam Suf, Matan Torah, and ate Manna?they should have rejoiced that they received more Mitzvos.- PF.
Hashem was angry because their cries were based on Ta'avah, which is a bad Midah, 1
Refer to 11:10:151:3. See also Oznayim la'Torah DH 'Bocheh le'Mishpechosav #1.