Why does Mr. Dussel cause Peter to become furious in The Diary of Anne Frank?

Peter is angry at Dussel because he says that someone ate his cat Moushi. 

Most of the altercations between Peter and Dussel are about Peter’s cat.  Peter brought the cat into hiding with him, and he loved it very much.  From the minute Dussel first found out about the cat, he was upset.  He claimed he was allergic.

Peter made a fool out of Dussel by pretending he was holding a cat under his...

Peter is angry at Dussel because he says that someone ate his cat Moushi. 

Most of the altercations between Peter and Dussel are about Peter’s cat.  Peter brought the cat into hiding with him, and he loved it very much.  From the minute Dussel first found out about the cat, he was upset.  He claimed he was allergic.

Peter made a fool out of Dussel by pretending he was holding a cat under his coat.  When Dussel acted sick, Peter revealed that he wasn’t even holding a cat.

DUSSEL. [Still wheezing.]  It doesn’t need to be the cat … his clothes are enough … when he comes out of that room… (Act 1, Scene 5)

Mr. Van Daan tells Dussel that they are getting rid of their son’s cat.  He doesn’t like the cat either, feeling that the cat eats their food and Peter spends too much time with it.  When Peter objects that he only feeds the cat scraps, Van Daan says the cat “looks better than any of us.”

The cat does disappear, however.  Peter is distraught, and Dussel has no sympathy.  When the cat has been gone for a week and Miep can't find it, Dussel tells Peter that someone probably ate it.

DUSSEL. Make up your mind, already someone has had a nice big dinner from that cat! (Act 2, Scene 1)

Peter is “inarticulate” and furious at this comment.  He acts as if he wants to hit Dussel, but Mr. Frank praises the dinner to “ease the situation.”  Things just get more tense, however, when Peter says that his father is going to sell his mother’s fur coat.

With this many people trapped in a confined area, conflict is bound to occur.  Mr. Dussel did not get along with either Anne or Peter.  Both disliked his bluster and rudeness.  He was just another adult to tell them what to do in a house where adults outnumbered kids.