There aren't many instances where you could get away with bringing your own instrument to a gig and expect it to go well at all, but in a super-chill environment like a Jason Mraz concert, anything can happen apparently.
Jason fan Stan Chou was at his gig at the TIPP in Taipei in late November, and made the effort to bring along a shaker. He busted it out during "Be Honest", and caught Jason's eye - who immediately quipped "You're probably annoying all the people around you, so come up here," pulling Stan onstage to accompany him for the rest of the song.
Stan takes absolutely no time to get into the swing of things onstage - it's the first time we've seen someone put their hips into playing a shaker. He even gets a little more bold and edges up to the mic to sing along with Jason, and that's where things get awesome (spoiler: there's harmonies).
You can check out the full thing below in a gloriously high quality. None of that shaky phone footage nonsense in Taipei.
According to a friend commenting on the video, Stan's a mega-Mraz fan and a talented singer in his own right. Check out this live performance of him and his friends covering "I Won't Give Up" on his YouTube channel (Sadly there's no appearance from the shaker).