It is possible to celebrate Xmax inadvertantly, so if you're having quite a lot of fun at Xmas and nobody's talking about the baby Jesus, then you're probably celebrating Xmax. Don't worry tho, Xmax is much better.
"Yeh, I know. Thanks for this amazing present by the way, it's much better than any Xmas present i've had before!"
"That's cos it's an Xmax present dude! Merry Xmax"