After an enthusiastic start, he found himself hanging awkwardly from the attraction in Victoria Park, near the Olympic venue, shortly after celebrating Team GB's first gold medal.
It's not the first embarrassing blunder involving the eccentric politician - in 2009 he was snapped falling into a river at an event promoting the work of volunteers.
With a catalogue of such slip-ups behind him, it seemed almost unfair to pick on Boris as the subject of a further caption challenge (you had some great suggestions for this picture on Olympic security) but we liked this week's photo so much that we couldn't resist, and we're sure that you will come up with some witty words to match it!
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There are no prizes, this is just for fun. If you have an idea for a caption, please submit it using the comments box below.
(Unfortunately it is not possible to access our comment facility from mobile devices at the moment. We are working to improve the technology and hope to have this option available shortly.)