Surprising things that are not vegan-compliant

The colour red.
Bandages.

Most vegans don’t eat honey, and do eat almonds, despite the fact that it’s easy to buy local honey from bees that are basically pets that could fly away at any time if they weren’t happy, and almonds are pollinated by enslaved and abused bees that are shipped across the country and suffer a lot of mortality (whole hives dying) from the stress.

As said above, you have to draw the line somewhere, and there’s a lot of benefit in all using the same standard.

The non-vegan food that surprised me the most was white sugar. But it turns out that even though most sugar isn’t certified as vegan, it’s becoming uncommon to use animal-based charcoal in refining it. I’ve seen websites that help you read the labels on ordinary brands of sugar to decide which plant it was processed in and thus whether bones were involved.

Yeah, I think the use of bone char in sugar refining was more of an advantageous use of a waste product, than it was anything to do with the very specific suitability of the material.

The general rule is that the animals were not killed by or exploited by humans. If it died a natural death, it’s considered okay. Because no human contributed to that animal’s suffering.

Nobody’s mentioned Jell-O yet?

Polymer banknotes as used in the UK, Canada and a few other places, contain beef tallow.

Probably because it’s not “surprising.”

I know a vegan who ate unfertilized eggs from their roommate’s pet chicken.

I doubt vegans eat carrion, not even when no human was responsible guilty of the death. Vultures are not generally considered to have a vegan lifestyle either.
kayaker has already mentioned isinglass as clearing agent for wine and ale (and other types of beer and champagne, I would like to add). In some regions like Spain often egg white is used as clearing agent instead of isinglass, which is also not vegan. In those regions the remaining egg yolks are often widely used for all kinds of very yummy sweets. Yemas de Santa Teresa is a typical example: very sweet, very tasty and full of cholesterol:

Others simply make eggnog, advocaat or Eierlikör, which essentially the same stuff with different proportions of egg yolk, sugar, and alcohol.

I definitely know of some who have. But, of course, most don’t actually have a taste for meat. And it’s difficult to catch carryon when it is appetizing and safe to eat. So it’s obviously quite rare.

It doesn’t really change the general ideals of what veganism is. People act like it is unknowable, but seem to forget veganism has a clear origin and a society that established the baseline rules.