lark it up

Also, lark about. Have a noisy, exuberant good time. For example, We were larking it up when the supervisor walked in, or He's always larking about at night. These expressions employ lark in the sense of “to frolic,” a usage dating from the early 1800s. Also see cut up.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.