Tom is described as a dirty, unpleasant person, using the metaphor of a pustule to emphasize his unappealing nature. This characterization suggests that he may be a negative or untrustworthy character within the story. The description paints a vivid picture of his unpleasant demeanor or appearance.

The quote, "Tom is a filthy little pustule. If you quote me, I'll deny it!", highlights a humorous yet slightly harsh tone. It suggests that the speaker is warning others not to repeat this critical opinion about Tom, perhaps indicating some conflict or a need to protect Tom’s reputation, despite the harsh words. This quote is from Nancy Farmer’s book, The House of the Scorpion, which delves into complex characters and themes.