This happened on a 159 when it was raining last week.
Guy gets on with a big golfing umbrella. Stands in the aisle and doesn't put the umbrella down.
The people getting on behind him can't get past and tell him to put it down. He airily tells them he can't put it down, it's broken, but does have the decency to move down the aisle a bit. Now he's blocking the stairs, and the people coming down them can't get off. He explains again that he can't put his umbrella down, as it's broken.
People coming down the stairs fight their way over the umbrella, and get all tangled up and cross. The bus driver stops the bus and tells him to put his umbrella down. He (slightly exasperated at this point) explains again that he can't put his umbrella down, as it's broken.
Facing the wrath of the bus (except me, I was pmsling), he gets off... but leaves his umbrella in the aisle.
The driver leaves his cab and he and a passenger try to fold in down (with limited success) and manage to manhandle ito out of the back doors. It springs onto the pavement like a big stripey bird and there it remained, until the other day.