Mayim Bialik -- The Worst Part About My Busted Hand is ...

"Big Bang Theory" star Mayim Bialik and her banged up right hand were at LAX last night ... and she revealed to TMZ the ONE THING she can't do anymore ... and it's kind of gross.

The former "Blossom" star was leaving the airport -- still sporting an arm sling and bandaged digits, after a bloody car accident two weeks ago left her with some pretty brutal hand injuries.

Mayim says she's doing fine and she at least "made it through the flight" -- so we ask her what is the ONE THING she misses doing with her right arm most ... and you gotta check out her answer because it's pretty amazing.