Oddly good show from Freakonomics. 

I had a Jarisch–Herxheimer reaction to the beta-lactam cephalosporin antibiotic Cephalexin when I was young, and then told I have a penicillin-class allergy by a tard doctor. 

I’ve since taken amoxicillin with no issue, and this is purportedly the case for ~90-98% of people told that they have a penicillin allergy.