I really detest onion on my burgers, but like most people on this thread have little to no faith in a custom order being put through correctly - once I asked for no onion on a McD's Quarter Pounder and bizarrely got extra lettuce instead, which it doesn't actually come with in the first place!
However, I have found that asking for a burger "plain" with nothing on it seems to work - they'll actually get that order right 99% of the time. So I do that and then ask for a pot of ketchup/mustard/BBQ sauce/whatever condiment I'm in the mood for, and put that on myself.
Oh, but when I am in the States, I always add cheese to a Wendy's Spicy Chicken. Just because I can.
I have no idea why, but something similar to the Magically Disappearing OLN has been going on with one of the TV's here. The one that's not hooked up to digital cable (as in, the old-school box) can't get the local Fox affiliate.