There’s a tie for first place.

• Marriage can be plenty stressful with just one partner. “He had seven hundred wives and three hundred concubines [secondary wives]” (1 kings 11:3).
• In his old age Solomon worshiped idols.

Actually the tow dumbnesses were connected. Solomon married foreign women as part of peace treaties and trade deals. A foreign ruler was less likely to attack Israel or renege on a trade deal if his daughter was living in the harem of Israel’s king.

Solomon’s brides, however, didn’t just bring their baggage to Jerusalem: they brought their gods, as well: “In Solomon’s old age, they turned his heart to worship their gods instead of trusting only in the Lord” (1 Kings 11:4)