Malapropisms - symptoms of what?

The American Heritage Dictionary definition:

mal•a•prop•ism - n. - A ludicrous misuse of a word. (After Mrs. Malaprop, a character in The Rivals, a play by Richard B. Sheridan (1751-1816).

This past weekend, one of my friends regaled me with two of best ones I'd heard in awhile: 1) She was jokingly talking about taking revenge on someone. She said that she would make a "mazel tov" cocktail to throw at them. 2) She knows that I have a special type of bicycle. She asked whether I had ridden my "incumbent" bike to my destination.

I don't recall hearing malapropisms from her before - so naturally, I'm a bit worried that they might be a symptom of an as-yet-undiagnosed health condition. I certainly hope not - I'm rather enjoying the laughs - and can't wait to hear the next one!