Ok, so not other answers so. . It is a silly, fun, thing to say. . Cheezy, as you said is a silly, not so attractive things to call something or someone. . If called, cheezy, someone might have a response of some kind. . This is one such response. It implies that there is some skill involved in being as they are. . It is no easy to look/act like this. Not a serious nor formal thing to say. . Probably never here this said out loud in your lifetime.

It's a really silly phrase. I think it came from a Cheetos commercial in which "It ain't easy being cheesy" was the catchphrase. ("Cheetos" being a cheese flavoured snack.) It can also be said to someone as a joke if they did something really cheesy. As others have said, you won't come across this phrase much.

This phrase? Used once ever.