Every semi serious cycling twanker and his dog is buying magic shine clones on the bay and then tootling down the towpath with them.
It's considered polite to turn these things off when you are head on to other peds and cyclist, perhaps have a slightly less bright head torch so you can kill the main beam and carefully make your way past people, perhaps even fit a bell. It is not however considerd polite to hurl abuse and threats when people suggest that you point it down a bit or turn it off until you have safely passed people - it may in fact even lead to nose bleeds and dental problems if you continue with such behaviour as not everyone is as forgiving as I am - like the fat middle aged king of the hi-viz decided to do last night.
May he fall arse first on his pump and get it stuck there.