What part of the Anne Frank's diary suggest that human beings continue to be petty-minded even in the most trying circumstances?

Anne Frank: The Diary of a Young Girl clearly shows how even in the most horrific circumstances, humans can still argue about silly and unimportant things. Naturally, being stuck together with 7 other people in a tiny apartment for years at a time without being allowed to go outside would bring out the worst in people.

The truth of this is clear from the seemingly ceaseless bickering and grudges held by the different members of...

Anne Frank: The Diary of a Young Girl clearly shows how even in the most horrific circumstances, humans can still argue about silly and unimportant things. Naturally, being stuck together with 7 other people in a tiny apartment for years at a time without being allowed to go outside would bring out the worst in people.

The truth of this is clear from the seemingly ceaseless bickering and grudges held by the different members of the Secret Annex. When Mrs. Frank receives extra sugar from Mr. Kugler on her birthday, Mrs. van Daan is angry that she got no sugar on her own birthday (page 167). Dussel treats the van Daans to unexplained, moody silences for no apparent reason (page 146). The Franks and the van Daans separate more and more of their food items from the communal stash over accusations of unequal sharing and disagreements over proper cooking (page 166). At one point Anne asks, "Are most people so stingy and selfish? I've gained some insight into human nature since I came here, which is good, but I've had enough for the present" (pg 167). 

Still, even though Anne participates in her share of quarrels and bickering, she also often reflects on the ungratefulness that this suggests about her, and the other members of the Secret Annex:

"Why am I often so miserable  about what goes on here? Shouldn't I be happy, contented, glad, except when I'm thinking about Hanneli [one of Ann'e Jewish friends] and those suffering along with her? I'm selfish and cowardly" (page 154).

If Anne feels this way, she is likely not the only one. Despite the petty-mindedness displayed in the diary, there was likely much gratitude as well, even if it was buried under the surface.