The phrase "Can you believe ___?" is used to criticize something that you don't like. For example:

Can you believe he didn't even call me back?

Can you believe this shit? I've been waiting for over an hour!

Use "Can you believe ___?" when you think people are doing something that's totally unacceptable, and you're surprised about it. You usually say this to someone who you think will agree with your opinion.

"Just (did something)" is often used along with this phrase:

Can you believe she just took it without asking? How rude!