As a kid, if you'd give him something with RD2 in it, he'd literally bounce off the walls for a couple of hours until he exhausted himself.
Not life-threatening, but a real PITA for his parents. You'd be amazed at how much stuff has red dye in it.
To make the obvious parallel here, I am totally glad that the way your cousin's parents dealt with it was not to deny the use of the dye to everyone else in the country.