Worst burn I got from snorting a drug/pill was a Ecstasy pill, it was green and I don't really remember anything else about it, except I believe it was double or triple stacked. I snorted half and ate half and it burnt for about 15 minutes. Then I was rolling hard and if there was pain anymore I didn't care about it. It was some of the best E I ever did. I am not sure what caused it to burn to bad.
The burn was not all that bad, not like I was in agonizing pain or anything. But as far as I can remember it burnt much more than anything else I ever snorted.