I have never really used a safeword. I have had one once, but it was never used. The word then became an inside joke between me and the people I used it with. The word was tricycle, and it was to be used in a somewhat threesome that I was in a couple years ago (a different post, I promise).
I know a lot of people use words like “orange” or “red” as their safeword. I am not sure how we came up with tricycle. I think it was just the fact that there were three of us, and we were trying to find random words that were unique enough to remember in the heat of the moment.
Our safeword never got used, but it sure did get made fun of. It became our inside joke when one of us would come up to the other (two) and say “I want to ride your tricycle.” No one knew what the hell we were talking about, it was great.