Well Stroppycow was closest in answering how I got a small bruise on my left knee. The small grey thing that you can see in the photo is the control unit for the sat-nav system. It's placed just where I brace my knee when I go around a corner a bit fast, so that I don't slide all around the seat.
Thanks to those of you who suggested that I might have gotten it because of having wild (and weird) sex with nurses. Sorry to disappoint, but even if I were having sex, sex with me tends not to leave bruising… Just satisfaction.
(Well I'm normally satisfied…)
I do get an injury from carrying my huge and heavy response bag, but it tends to be bruising on the shoulder from where the strap rubs, or wrenching of the odd muscle from catching it on someones radiator.
I think that when the fitters are done checking my tyre changing work, I'll see if I can head down to the computer people to get the handset moved.