Regarding public speaking:

As you know, I work in a transportation-related occupation, so obviously I have to abstain from drinking except on weekends and even then in moderation.

However, for humorous effect, I once started a meeting with other transportation people by saying, "Hi. My name is Sarah and I'm an alco...oops. Wrong meeting."

I thought it would be funny, given the contrast with my (known) normal lifestyle and the implication of the words.

Nope. They took me seriously and had me investigated.

From that day on, I've played it straight. No humor in public appearances for me, unless they are informal gatherings. Whew!