What was the worst bitcoin bear market?
2011 or 2015.
Bitcoin's first bear market in 2011 was also its worst based on the total percentage drawdown in price. After its then-all-time high around $29, the price of bitcoin fell more than 90% in less than six months.
Bitcoin's worst bear market based on length was the drawdown from 2013 to 2015, which lasted 411 days. Not only was that the longest bear market ever, but it was also the second-worst drawdown. Bitcoin's price dropped 84% during that period.