Bruce Springsteen -- Jumps Into Crowd, CHUGS FAN'S BEER

Bruce Springsteen is the most easily-poisonable rock star on the planet -- because Tuesday during a concert, he grabbed some stranger's beer in the crowd ... and CHUGGED the entire thing ... no questions asked.

It all went down during the Wrecking Ball tour in Philadelphia -- The Boss jumped off stage .. beelined for the crowd ... and sang "Raise Your Hand" in a sea of grab-happy fans.

Then the magic happened (skip to 1:30 in the video) -- halfway through the performance Bruce sat down and a grateful fan handed him a pint of beer ... then like a BAD ASS … Springsteen chugged the golden elixir, threw the empty cup to the crowd in triumph and continued to perform without missing a beat.