Boar Agression

Question
We have 2 male Guinea pigs that we got from the animal shelter. They are not in the same cage due to the fact that the older boar (Phineas) starts chattering teeth only when they are in the same cage together. They get along outside the cages and they will groom one another outside and in some cases if they are in the younger boars (Buddy) cage.

Recently we had a friend watch her 2 females because of flooding and wanted us to breed them with our 2 males. Phineas wanted nothing to do with either girls, but when the one female (Honey) began trying to mount the other female (Krinkles) I took her and put her in with Buddy. They did their thing and enjoyed each other company for a few days. She didn't want to go back in her cage and would chew on the caged and be aggressive towards Krinkles. But now that the 2 girls are back at their home, Buddy has seemed more aggressive towards us. He doesn't want to go back in his cage after being out and instead if his nibbling on our fingers he has been actually biting. I was wondering why he is being this way.

He has bit me once before this, but he had reason too and I deserved it so I never got mad at him for that. He warned me and I ignored it, but now he is doing it to my daughter when she is trying to take him out of his cage, which she has done all the time in the past and he always let her pick him up.

Answer
sometimes they do turn more aggressive once they are in "breeding mode" this is not a fact just my observation and theory but once they have been with a female i think they sort of mentally get their act together and get more aggressive because they have to defend their position.
also when you introduce any new pig to one or more exeisting pigs the entire social dynamic changes and a bit of fighting breaks out while the heirarchy is established. my assumption is he will act like this for a little while but things will eventually go back to normal.

hope this helped