User cachecrab on Twitter noticed that Google has a rather unusual interpretation of the query “20% of £1k”.

@robinhouston reminds me of a friend who once asked Wolfram Alpha for a graph of "tan tan x", and got a graph of tan x, drawn in a light brown colour.

I think they fixed it, though. (Disappointingly.)

@simontatham Wolfram Alpha used to have some utterly hilarious misinterpretations! I wish I could find examples.
@robinhouston @simontatham this is the one I remember quite well:
@tpfto @robinhouston @simontatham Dwarf Fortress when a dwarf tries to punch and kick a megabeast.