Chances are you've never heard of Alive Day, a very personal observance by a very personable young Washingtonian named Jim Mayer--and one he shares as the host to dozens of friends.

To the 39-year-old Mayer, Alive Day is April 25, the anniversary of that awful day in 1969 when, as a corporal in the 25th Infantry Division, he stumbled upon a booby trap in Vietnam that set off enemy mortar fire and blew off both his legs.

Astoundingly, some might think, Mayer annually marks the event, as he did Thursday evening for the 16th consecutive year, with a party at Ireland's Four Provinces, a Connecticut Avenue pub. The master of ceremonies was John Fales, a blinded Vietnam vet.

"I knew I was going to make it," Mayer told Metro Scene yesterday, saying he decided then that "I would celebrate it every year. It's a simple statement, that I'm glad I'm alive, and I'm glad my friends are, too."

Mayer, who comes from St. Louis, became executive assistant to Max Cleland, President Carter's head of the Veterans Administration, and now is staff administrator for the Paralyzed Veterans of America.

He walks on artificial legs and -- hey! here's some great news -- in July, he's marrying Debbie Spittal of Reston, originally of Cleveland.