The first pasuk of Parshat Noach states: אלה תולדות נח נח איש צדיק תמים היה בדורתיו.... Rashi comments on בדורתיו by saying that there are those Rabbis who explain it as praise, meaning that Noach should be praised, for even if he were in a generation of tzadikim, he would be an even greater tzadik. There are those who explain it derogatorily, saying that if he were in the generation of Avraham, he would have been nothing. How can we understand the opinion that he would have been a greater tzadik in the time of Avraham?
Take, for example, a class in school. If most of the class does not study for a test and they all get fifties, and one student studies and gets a sixty five, you can say he looks better than the rest. However, this is only relative, because everyone else did so poorly; if he were in a good class he would not be anything. Or you can look at it by saying that if he were able to fight peer pressure to study and still get a sixty five, he would have done much better in a class where he had the reinforcement of others wanting him to do well. We can understand the praise, that Noach would have been an even greater tzadik in a generation of tzadikim.
Interestingly, Rashi seems to follow the derogatory explanation, comparing Noach unfavorably to Avraham; whereas the Radak chooses the favorable explanation. Rashi explains that Avraham did his good deeds spontaneously while Noach only followed Hashem's commands. Radak explains that Noach followed Hashem with all his might and suppressed his nature which would have been to fall in with his peers.