AMAZING!!!! I thought for certain I was crazy or just flat out wrong, but I have the exact same problems you describe. I'm not even sure what this forum is actually for, but I simply had to register to talk about this!
Just like you state, almost instantly after eating eggs, or avocado, prepared in certain ways..... I get a horrible feeling in my stomach. I can only describe the feeling as a cross between passing out and vomiting, without the actuality of either of those happening. It basically takes all desire to eat anything completely away from me, regardless of how hungry I may be. After 10-15 minutes my appetite returns and I can eat an alternate item.
And also, just like you said, sometimes either one is perfectly fine. I don't seem to ever have the issues with items prepared with eggs, and sometimes I can eat eggs just fine. It's crazy.
Glad to hear someone is screwed up like me!
PS. I do not suffer from Touretes, or basically any of the other afflictions discussed on these forums.