Sanhedrin 108a: Noach told his generation that if they do not repent, Hashem will bring a flood, and your bodies will float on the water like pouches.

Rashi: Noach and Mesushelch warned them that a flood will come against them. They said, we are light - we can swim on the water. Also, we have light substances like reeds to make boats to float on the water!

Ibn Ezra (14): Hashem will make them like something light, that floats n water.

Malbim: This discusses pirates, who go in swift reed ships to plunder seafarers. Also they distance from people and destroy civilization!

Sanhedrin 108a: Noach warned his Dor, people will use you to curse ('you should be punished like Dor ha'Mabul'). They scoffed 'if you are right, why doesn't Hashem bring the flood right away?' He answered, He wants to take one Tzadik (Mesushelach, in his proper time) first, lest he be punished with you.

Rashi #1: They cursed their portion in the land, and said 'we will not go in the ways of Tzadikim.

Rashi #2: Keramim are Tzadikim. They swore that they will not change their ways [to go in the ways of Tzadikim].

Rashi #3: Their portion was ruined. They would spill their seed l'Vatalah - "Hishchis Kol Basar Es Darko." Tekulal is an expression of ruin - "ba'Avon Asher Yada Ki Mekalelim Lahem Banav."

Rashi #4: I heard, Doros after them will curse 'the One who punished Dor ha'Mabul, He will punish...'

Rashi #5: They did not accept rebuke from good people.

Rashi #6: They were light to go in boats to kill and extort money. In settled places and vineyards, there is no concern for this.

Ibn Ezra: Not one of them will turn to the vineyards (be saved). They, their fields and vineyards will perish.

Malbim: Their portion in the land - fields and vineyards, is totally cursed. They never come to them. They are further from people than plunderers of the Midbar.