He really doesn't give a shit about that. He's annoyed that Lazarus is being an idiot and trying to rush things without thinking.

Joshua is hot-blooded (He was raised by Vikings in the first half of his life for Christ's sake) but he can temper himself thanks to his training in the far east and knows when to keep his calm.

Though his tongue is about the only thing he doesn't bother to restrain for the most part. He'll tell ya exactly what he thinks about people or situations.