Bingo!

The inflated jeans trick makes a nice YouTube stunt in a warm, calm pool, but I question how practical it would be in a real deal emergency? Consider that in most cases one would be wearing shoes or boots, which you would need to take off before you could start to take the pants off. Then you need to get the pants off. Then you need to knot both legs. Only then can you get some floatation.

Even slightly cold water will rapidly sap your strength and dexterity. Even moderate wave action will also make this harder. I would like to see a video of someone jumping fully clothed (including shoes) into 60 F water with a stiff wind kicking up a 2ft chop, and making this work. Until then I'm skeptical.

The best advice is still to wear your F-ing PFD!