London — Hundreds of Londoners headed down to the Underground on Sunday afternoon, stripped down to their underwear and travelled around a bit, trying to look as though nothing unusual was going on. As if. This was the Official No Trousers Tube Ride, an annual event with no point other than injecting a little levity into the bleak midwinter. No deep meaning, no bigger motive. The only goal was to be silly, if but for one afternoon. “There’s so much bad, so much not fun going on,” said ringleader Dave Selkirk, a 40-year-old personal trainer. “It’s nice to do something