business expense vs. personal expense

the characterization, as 'business' or 'personal,' of the litigation costs of resisting a claim depends on whether or not the claim arises in connection with the taxpayer's profit-seeking activities. It does not depend on the consequences that might result to a taxpayer's income-producing property from a failure to defeat the claim

Defined by the Supreme Court in - United States v. Gilmore, 372 U.S. 39 (1963).