A car dashboard used as a drum.
Despite our enthusiasm for the trip, keeping it interesting for the duration of the drive proved challenging. We listened to a book on tape. We played dashboard drums in time to the Backstreet Boys and stuffed ourselves with sinfully delicious snacks.
Robin Spevacek, "Thief River Falls, Minn.," Star Tribune, January 7, 2001
The album liner notes gives Hahn credit for 'dashboard drumming,' on the song, which relies mostly on a programmed hip-hop style beat.
—Michael Mehle, "Drummer taps into success of Geggy Tah," Denver Rocky Mountain News, October 18, 1996
I suspect drivers have been tapping out rhythms on their dashboards and other resonant car parts since the first car radios were installed. I also suspect that more than a few people coined the attractively alliterative phrase dashboard drum (or dashboard drumming) over the years. However, the earliest citation I could find was a reference to the liner notes of an album called "Sacred Cow" that was released in 1996 by the band Geggy Tah
The predecessor (and often bandmate) of the dashboard drum is the air guitar, "an imaginary guitar that a person pretends to play, especially to mimic the actual guitar sound in a rock song." This phrase dates to 1982:
It was 'air guitars' night at the University of Alabama, and students called it the greatest rage since streaking.
'I never saw anything like this,' said awed spectator Rebel Steiner.
The object of an air guitar act is simple: you get on stage and pretend to be playing a musical instrument. Some performers used props such as broom sticks, tennis rackets and cardboard.
"On the Light Side," The Associated Press, April 24, 1982
Many thanks to Word Spy subscriber Rebecca Lyn Hepworth for drumming today's phrase into my brain.