When I eat peanuts for some consecutive days, I get hemorrhoids or at least a hemorrhoid-like painful protrusion that lasts up to a week. I can't find info on this anywhere. What kind of bizarre allergic reaction is this? I don't have any other allergies that I'm aware of.

All I can think of is the high arginine content of the peanuts are increasing arterial blood flow, which means more blood being returned in the veins.  The excess blood in the veins can be increasing pressure in them flaring the hemorrhoids.

Generally peanuts are suppose to help with hemorrhoids due to their fat and fiber content, but you are not alone by having flareups with peanut consumption.