I can beat that.
The computer rooms, (each 40 foot square), in a brand new PFI school had their power sockets spaced round the walls, every two metres as per normal, but all the network sockets placed in the trunking run down from the ceiling. Problem was, all the backbone cable had been specified as cat 6, & the contractor thought he'd save a few pence on the quote.
Thing was, no one had spotted this, & it was only when yours truly was allowed to look round the school, & saw it was it deemed incorrect, even though other members of the party, had been round the school, & had been on the planning committee.
Another factor that magnified the ouch factor, was that the school was built as two wings of three floors, off a central hub. Originally the plans, negotiated by someone who was IT knowledgeable, had called for a network & power closet half way down each of the wings, however, the contractors had managed to get that overturned, & had had a single closet put on each floor of a the central hub, & don't get me started on the planet switches stacked 14 high!!
(Icon for what happened to the network, despite my warning, when everyone logged on at once.)