Take a DEEP breath, next time pass on that extra cup of coffee.

I have been traveling with dive gear and bicycles on AS for years, NEVER had ANY issues. Just make sure your bags pass the reasonableness smell test (figuratively). Be prepared to be questioned if you present a generic duffel bag that is overweight/oversized for the dive gear exemption - better to use something that is obviously intended for the purpose. I would have the BCD, fins in an easily accessible, conspicuous location to show the ticket agent in the event there is a question.

Ticket counter agents have better things to do than crawl around your bags - leave that to the TSA. Best to leave the attitude at home and start vacation mode before arriving at the airport - will not serve you well when speaking with the gate agent.