The insult is reminiscent of the Australian veteran's ridicule of "first lap nutcase" Romain Grosjean last year.
His angry jibe at van der Garde, a rookie this year, follows an incident in the Canadian grand prix, when the Red Bull and Caterham collided while Webber was lapping the Dutchman.
Webber was unimpressed with van der Garde's talents.
"We had a lot of blue flags as we approached the hairpin," he said. "Some guys maybe have too much concentration on (just) driving the cars."
Van der Garde, 28, was penalised five grid places for Silverstone, and apologised to Webber in the post-race team press release.