Meaning of "Real knicker-rotter" [closed]
I found a copy of the text online. I am reluctant to link to it for copyright reasons. The relevant text appears to be a line spoken by a character called Roy:
Come on. Let’s go into the kitchen. I’ve made a special champagne punch, Aggie. It’s a real knicker rotter.
This is a scene set at a party. I am not aware that "knicker rotter" is standard slang. (An online search seems to produce only references to the novel or people asking about it.)
The implication is that the punch is very strong. I can think of several reasons why the phrase might be used to mean that, with various degrees of vulgarity. Perhaps the least vulgar would be that it might cause the drinker to become so inebriated that they wet their underpants (knickers). There could be sexual innuendoes as well.