If a vegan eats out with someone who orders a non-vegan meal, would it be contradictory to veganism if the vegan invited this other person and covered the expenses for that non-vegan meal? Would it make a difference whether the vegan announced his payment before or after ordering the meals?
Generally speaking, covering a non-vegan's meal expense does not sit right with me, and technically certainly is not vegan. But I feel there is a time to make an exception.
I have a house rule of no meat allowed into my home. This is non-negotiable, as it is my safe zone. But when I am at a restaurant, eating from cookware that also cooked meat, trusting a cook that may likely not understand veganism, concessions have already been made. We all live in this reality.
But I don't think the purpose of veganism should be to make yourself as pure as you can be. It's not about you, it's about the welfare of animals, and converting one other person to veganism will do more than a lifetime of personal obsessing.
Eating out is our culture's most common form of socializing. Often as a social grace, one offers to pay for friends, and they return the favor another time. I think this is a very nice cultural habit. But as hunger pangs set in as you browse the menu, the people you go out with will order what they like. It's not a good time to try to convert anyone. Rather, offer to buy their meal, that they would have paid for anyway, to show them that vegans are rational, reasonable, generous and have at least an occasional capacity for something other than complete judgement and condescension. You'll be amazed at the effect. I have converted more friends with this approach than any other. The next time out, your friends might even try the seitan. :-)
I absolutely agree with Pyloid that you should maintain your vegan ethics when buying gifts for others. Also, there is a time and place to sell the whole deal. Younger people who have not become ingrained in their habits, or the more open-minded lifelong explorer, may be ready for the full slaughterhouse video assault. The raw truth is still the most important thing. I used to stuff this truth in others' faces, social order be damned, and it felt good. I'm just not sure that always has the best overall outcome.
I say that it depends on the details, and there is a time and a place to offer to pay. This is VERY MUCH my personal opinion, though, and I respect dissension.
Veganism isn't about just eating plant based food, or avoiding leather, it's about avoiding animal exploitation whenever and wherever possible. I believe this extends to gifts and food you buy for other people. Obviously it's partly a judgment call though. Further examples, while I think donating to a charity which may inadvertently exploit animals is probably okay (AKA a soup kitchen) I think things fully in your control like buying food for others should be done "vegan-ly".
I think it's important to add, in my experience, this usually ends up less awkward than you would fear as long as you manage expectations, let them know ahead of time you'll only pay for vegan items, and as long as they understand your feelings on the subject, it should be fine.
That being said, if it's a first date scenario or something for business, it's obviously more complicated than if it's just a friend, in which case giving advance warning and being clear about expectations is even more important.