As you said above, the word "bob" means fencing and you want to know how this can have a double meaning related to homophobes.
This is what I see the 2 meanings as:
1. fencing, as in taking out your fencing sword
2. take out your penis, as penis would be another word for sword in plays/books such as the one you're reading - this would be relating to gays if the convo was btwn 2 men
I love this book!
But I am not sure what you mean with your question (it's missing a verb).
But if you're looking for more information: The sense of guilt in this book is often created by other characters, when they're trying to come to terms with some tragedy (such as many characters being blamed for Sophie Mol's death). So in a way, guilt can function as an explanation. But also it's created by the social norms (as when Estha feels guilty because of the Orangedrink man).