This kind of thing happens to me all of the time:

One day, we were learning about STDs (sexually transmitted diseases) in my Human Sexuality Class, far out, baby! My teacher wrote STDs on the board and I said, "Goody! We're gonna learn about venereal diseases!" and my teacher said, "They're not called venereal diseases anymore." So I said, "But I dig saying venereal disease. See, 'venereal disease,' 'venereal disease,' it just rolls off my tongue!" My teacher gave me a funny look and said, "I hope not."