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The act of wearing a flashing red bike light on the collar of your shirt in a similar manner to a bow-tie.
"I am going to a rave tonight. I had better not forget my Clapham bow-tie"
by Domingo Cortez March 19, 2009
Wearing a rear bicycle light in the same manner as one would wear a bow-tie. Light is generally attached using a clip to the collar. Light is switched on/off as desired. Must be flashing when on.
'I say Jenkins, that chap is sporting a rather fine clapham bow tie, what?'

'Eeey blud, set me your clapham bow tie. Also your phone.'
by Dr. Lady Lolbert Monkeybush March 19, 2009