Perhaps it could be about something stupid, like Tops thinking that his youngest daughter has been kidnapped or injured, only to find that it was all a big mistake. Or maybe he could overreact...
(Littlefoot is playing a game with the rest of the gang, when Cera shows up. Unknown to her, Tricia has followed her, and the hatchling attempts to play the game. This leads to a minor accident in which a "pinecone" hits Tricia on her horn, very slightly bruising her, and making her cry. Tria and Tops rush over.)
Tops: Oh no! Tricia. What did you do to her, longneck?!
Littlefoot: I, we were playing a game and-
Tops: And what?!
Tria: Calm down, Topsy. Tricia's okay, and I'm sure Littlefoot didn't mean to do anything.
Cera: Yeah, dad, it was an accident, and no harm is done...
Of course, it could be something much more serious... let's say that Chomper's parents tried to enter the valley to find their son, and on the way there, nearly killed Tria, Tricia and/or Cera in the process (needing to eat something after a long trip)...
THAT would give Tops reason to be angry...