I find keeping a low profile works better than standing your ground, whatever that means. Bring your own food every day, even days when you know lunch will be provided at a meeting, eat beforehand, take a little bit of as many things as you can and eat around what you can't. If anyone asks, you're not that hungry. You've already told them that you're vegan and nobody knows where the salad issue originated here but it's not worth pursuing unless you can check with whoever orders the food. If you can check with them then hope they're cool and the next time you have a lunch meeting, ask them the morning or day beforehand to do a favor for you and see if there is something on the menu they could order that you can eat. People like others more when they have done something for them (it's true!) so be apologetic and act like they're doing you a solid. There's not much else you can do except try not to stand out. With clients, I don't make it a big deal and usually neither do they. I generally have more issues with colleagues than clients. I don't say anything if at all possible to clients--if at a restaurant usually I try to order last (feign indecision or say you have a question), then ask or gesture over to the server for he/she to look at the menu where I'm pointing, and now that they're standing next to me, finally ask any questions or say any special requests quietly to them and not to the table. I never say I'm vegan. I don't bother asking for dressing ingredients or anything where the server needs to come back and give me more information, instead I will do something like ask if i can just have balsamic vinegar and olive oil only (and I don't give a crap about stuff like if a tortilla is vegan in these scenarios). This sounds silly but generally the rest of the table will awkwardly pick up conversation while you're sorting out your order and forget hounding you about what you chose. If you are traveling and asked where you'd like to go for lunch or dinner with colleagues or a client, chip in suggestions where you can generally eat something right off the menu--just about any Asian place, nearly any Italian place has pasta and marinara, Mellow Mushroom, Chipotle, etc.