Sounds In The Silence
Whilst Mr Thomas is locked inside the outhouse he observes that "there were sounds in the silence" which of course is ironic because it is not possible; the whole definition of silence is that there is no sound. What it likely means is that usually he doesn't stop and pay attention to what is around him as much as he is being forced to now which is why he can discern noise where there wouldn't otherwise be any.
Trevor's Background
The gang hate the traditional upper and upper middle classes and the way in which they have both money and superiority. In Trevor's situation this is ironic because he is really hating himself; he is from an affluent background and is the son of educated parents who encourage him to learn and pursue goals. He is the very type of person that he claims to hate.
Mr Thomas' Cheapness
Mr Thomas He is a skilled construction worker and therefore manages to repair the house very well, at least, as well as is possible with the limited supplies that he has after the war. However, he is no plumber and doesn't know how to plumb in a toilet. Consequently he still uses the outhouse toilet. He has money, and savings, but is rather cheap with it and likes to penny-pinch. He will not hire a plumber to put in an inside bathroom because he doesn't want to spend the money. This cheapness comes back to haunt him when he is locked inside the outhouse by the boys whilst they demolish his home. He has saved money on an inside toilet, but that has cost him his entire house.
Working Class Jealousy
The boys, and to a certain extent, the truck driver, hate the upper and middle classes for their assumed superiority socially. They also hate the way in which the upper and middle classes feel that they are "better" than the working classes. In the context of the story, this is ironic because the boys, and the truck driver, are proving that people like Mr Thomas are indeed their betters; Mr Thomas would never dream of breaking into someone's home and demolishing it, or laughing at someone to whom this had happened. He is showing that he is a better person than they are and this is the very thing that they are angry with him, and the people like him, about.
Working Like Creators
The narrative tells us that "they worked with the seriousness of creators" which is ironic because the boys are doing the very opposite of creating; they are destroying, being destructive of anything beautiful that they don't have themselves. They are destroying someone's home, someone's life. They destroy Mr Thomas' life, and so despite the fact that they feel they are "creating" something the very opposite is true.
