Xmax is a bit like Christmas, but not religious. It is the Xtreme version of Xmas and is way cooler.
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.
"I can't believe it's December 25th again so quickly"
"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"