Alcohol suspected, (I don't drink)
No one wearing PFD ( I always wear mine-- not wearing one is a clear indication of ignorance.)
Goofing around (hmmmmmmm I can't think of goofing around in a kayak, but I have done more than my share..... I need to keep this in mind)

Coast Guard accident statistics indicate not wearing a life vest increases chance of death in an incident 6 times
They point out that when there's an incident where one needs to put on a life vest, it's already too late, or it's a time consuming step during a stressful busy emergency.
I think I also remember alcohol being involved in 15 percent of incidents and is considered one of the leading causes of boating accidents.

We should all keep in mind that the PFDs we kayakers wear will not keep our heads out of the water if we are unconscious due to head injury or hypothermia.
If you've ever been in a life boat drill on a cruise ship and put on their life jackets, they're bulky and head encasing to keep one's head out of the water while unconscious.
Aviator life vests inflate, which I always thought should be an option for the one's we wear for kayaking. In the water, injured or shivering with rescue not imminent? pull the cord, inflate the neck support. At the very least one's corpse will be more presentable and more easily found. More likely you'll wake up in the arms of a Coast Guard rescue swimmer.