Christmas isn't the worst name. There's probably some teasing potential, but there's teasing potential with every name. I wouldn't say it's unusable. Obvious nns are
Chris,
Chrissy,
Christy,
Kit, etc.
I'm not religious, so I wouldn't use most of these, but...
Other holiday names:
Advent
Ash (
Ash Wednesday)
Earth
EasterEpiphany (nn
Pip)
Equinox *
Eve (
Christmas Eve, New Year's
Eve)
Friday (Good Friday, Black Friday)
Hallow (Halloween) *
Hanukkah
Holiday (nn
Holly)
Independence (4th of
July, nn Indie)
Monday (Cyber
Monday)
PatrickPentecost *
Saturday (Holy Saturday)
Solstice *
Sunday (Palm
Sunday,
Easter Sunday)
Thursday (Maundy Thursday)
Valentine /
ValentinaWednesday (
Ash Wednesday)
* = my favorites