If you followed the sad saga of UK Tesco last year, you would know that when people don't get it, they simply don't get it. Tesco was a plaintext offender who actually tweeted a response saying
@troyhunt Passwords are stored in a secure way. They’re only copied into plain text when pasted automatically into a password reminder mail.
That has since been retweeted more than 2000 times.
Beyond the problems apparent in that tweet is that many good people, including Troy Hunt, offered to help to Tesco improve their systems. Tesco never even recognized that they had a problem. Even becoming the poster child for cluelessness didn't seem to make them consider that they were doing something wrong.
Only after it became something of tremendous ridicule and hitting the tech press did the lead to some talk of investigation by the Information Commissioner's Office.
Tesco no longer emails or DMs plaintext passwords, but we have zero indication that they see any problem with how they are storing passwords.
So maybe you can point out the bad press that Tesco received and suggest that they might avoid that by trying to understand why having plaintext recoverable passwords is a bad thing.