More on Treading on One's Corns from Infoplease:

• Treading on One's Corns - Treading on One's Corns (See Corns.) Source: Dictionary of Phrase and Fable, E. Cobham Brewer, ...
• Corns - Corns To tread on one's corns. To irritate one's prejudices; to annoy another by disregard ...
• Dictionary of Phrase and Fable: T - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "T"