Many people are allergic to peanuts. It's not uncommon for people to have reactions to latex or certain metals. Even Penicillin and Codeine can cause serious problems in some people. But some people seem to have odd allergies, strange reactions to everyday or common items.
When I was going through treatment for Leukemia as a child, they discovered the hard way that I'm "allergic to blood" (It's not quite that simple, but that is what the doctors use when describing it). I can receive blood, but only after it has gone through a process that makes it safe because there are a few things in almost everyone else's blood that can harm or possibly kill me. It's a lengthy process, so if I need an immediate transfusion, I'm out of luck.
I also cannot have Aspirin for reasons I'm not entirely sure of. It's not an allergy exactly, but it can kill me (even children's aspirin). I find it incredibly amusing because it makes me a little bit like The Doctor (the character, not any of the actors) because he can't have it either.
I have an extremely high tolerance to most types of anesthesia. This isn't all that uncommon, but I've always found it a source of amusement when I'm being put under (usually for an endoscopy because of my bleeding ulcers and constricted esophagus) by a doctor who doesn't know me and they have to keep upping the dose. On multiple occasions I've had doctors joke that I must be a mutant like Wolverine. My main doctor who does the procedures has a fun rule, too: He plays "I Wanna be Sedated" by the Ramones. When I stop singing along, it's safe to proceed with the procedure.
I also have what I like to call "Mutant Spleen-lettes". I had my spleen removed during the time I was being treated for Leukemia when I was 4. Several years ago, I was scanned (MRI, I think?) and the doctor was worried when he found strange little masses and sent me to a specialist. It turns out that they are spleen cells (I think that's the term) from when I was still within the womb. Those cells all have the possibility to grow into a spleen, but only one does (or something like that, I can't remember the exact wording he used). Apparently after mine was removed, the others decided to try to grow. They aren't fully formed and they don't function, but they grew larger than what my doctors have ever seen.
So I'm curious, who else has an odd medical issue? I surely cannot be the only one.