How can I get my boyfriend to stop pouting when he doesn't get his way?

It is unbelievably frustrating. He does it so often.

If I tell him something he doesn't like, he turns into a 5 year old.

The other day, I told him I would be a little late getting home because my (guy) friend needed me to drop him off at work. He immediately started pouting. Also, if he wants to do something (anything, not something in particular) and I'm too tired to at the moment (full time student and I work. He doesn't go to school or work) he starts pouting. It drives me insane! I love him so much but there's nothing I dislike more than a whiny man. When his not pouting, everything is perfect.

How can I get him to stop this? Or how can I call his attention to it without pissing him off?
How can I get my boyfriend to stop pouting when he doesn't get his way?
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