The Slowest Thing in the Universe

We all know that light is the fastest thing in the universe, but what is the slowest? For many years scientists thought that it was second class post, but in the mid-eighties it was proved that the slowest thing in the universe is actually the person in front of you at a cash machine when you're in a hurry. Or at least, that's what we thought, but it now looks like we might have to revise that theory once more after unconfirmed measurements of call waiting times for HMRC indicated that time might actually be flowing backwards.