By far, one of the worst teams in MLS history were the 1999 MetroStars, Bora Milutinovic bumbled his way through a season which at one point saw the sad Metros drop 12 straight matches. A record that still stands today. Incredibly, 1999 saw the MetroStars break another bad record, they actually started a season winning and not losing their first 3 games as they did in the first three seasons. The MetroStars were so bad that the 1999 Kansas City Wizards team, that team that could not score goals, beat the MetroStars 6-0 at one point of the season. The Charlie Stillitano era would end and the MetroStars would have an amazing 2000 season before going dormant until the Red Bulls took over the club. https://us.bolavip.com/soccer/longest-mls-losing-streaks-20210215-0007.html
IIRC the end of the 2014 season for the Rapids was the worst run of form in league history, and the start of the 2019 season for the Rapids was the worst start in league history.