I got my 80 yr old father this as a gag gift. When he opened it, he got all embarrassed and immediately tucked it away. Later, I privately asked him why he got all weird about it, and I found out that he was under the impression that it was a sex toy.
My sister learned a valuable lesson this Christmas: If you let your older brother take an ugly picture of you, you will get it on a custom color-changing mug as a gag gift.