My kids have had Coke in their horn. I'm pretty sure my husband's had rum and Coke in his at some point. (Both is blaspemy, but then again, I've had some pretty odd stuff in my own horn, so I can't really complain...) Either way, it works fine. Some wine stains waxliner red, and coffee and tea melts it, but other than that, you can drink whatever you want in a waxlined horn. Not sure about that other finish that you can buy here (can't remember what it's called, but it's REALLY blasphemous! LOL).
I like my horns. Mead tastes better in a horn. Can't explain why.
We use a HUGE horn for our blòts, as we have a large number of people in circle and the horn needs to not run out of mead every two minutes. The opening end is like about the size of my (admittedly) skinny leg! My husband, who also doesn't like to run out of beer, has a huge horn. It's about the length of my arm and fits two beer at a time. His SCA name translates to "Desirous of Beer" in Old Norse for a reason. Mind you, the size of a man's penis extesion may be an indication of lack of real equippment, but don't tell him I said that. LOL.