Customer - "Your website isn't working"
Me - "Why"
Customer - "It's different"
Me - "What website are you using?"
Customer - "www.xxxxxxxx.com"
Me - "That's the wrong one. It's www.yyyyyyy.com"
Customer - "Oh yeah, that's right, silly me. Let me login to the website. I can't get in. The login details are wrong."
Me - "What are you typing in?"
Customer - "Username - xxxxx. Password - yyyyy."
Me - "It's the other way around. The usename is yyyyy and the password is xxxxx."
Customer - "Oh, yes, silly me."
Me (thinking) - "How can you be an IT teacher if you have trouble getting into a website, dumbass!"