i used to fill liquid nitrogen dewars on a regular basis and i did get to play with it from time to time. There are all sort of fun things you can do with cryogenic liquids.
Here are some of the fun but harmless ones.
Freezing insects is neat!
Spray a fine mist over yourself when your hot and sweaty you get fog rolling off of you!
Dip your co workers gloves in it and then shatter them!
Crack some types of rocks!
Freeze your coworkers lunch so solid it takes half his lunch time to thaw it out in the microwave!