I think you have to say Bitcoin. My approach is always, “Would you consider taking your tip in Bitcoin?” If they say no or are derisive, you just tip in fiat and move on. If they are interested, they will usually start asking questions. At which point, I tell them they shouldn’t accept Bitcoin if they need money today to pay bills. It’s something that should be put away for 5 years or more. This takes care of the conversion issue. Just my personal thoughts and experience.