I have had lads flicking their flights (makes the clicking sound), talking to themselves (trying to gee themselves up), tapping their foot etc, most of the time it is unintentional but on the occasion where it feels they are doing it on purpose I have in the past just stood back until they stop.
The annoying part is that they have got to me, they have disturbed my rhythm and they know it - but I have responded, by me standing back I have let them know that their antics are disrupting my concentration.
So, if they continue to do it (in my experience they never have after I have initially stepped back) I think you are within your rights to challenge them.
I have no problem with a nervous opponent flicking his flights, no problem with an opponent talking himself up - I think you can tell if they are doing it to directly put you off and many players will do it subconsciously.
Normally I am in the zone after the first leg and it would take something unusual or deliberate to break my concentration.