On the 4th of February last year, I started my current job. Our institute is spread across two sites, one in Chelsea, one in Sutton (Surrey). I diligently found my way to the Sutton site (I'd been interviewed at the Chelsea site), which considering I had a broken arm so had to rely on public transport, was no mean feat.
I called him from the train to Sutton, having got the 5:40 bus from Oxford, then a train from Victoria, to warn him that I was going to be about 1/4 hour late (assuming a 9am start time)... great start.
Then, when I got to reception, they put a call through to my boss, who said he'd come to reception to collect me. Unfortunately, he was in Chelsea, and I'd misread my e-mail, so I then had to get the train back up to Chelsea. The moment I realised what I'd managed to do was definitely an "oh shite" or EPIC FAIL moment!
Luckily, my boss is really cool, and while he still ribs me about it, things could have been a LOT worse!
:D
Roo