Touching your ears is old idiosyncrasy (4)
I believe the answer is:
otic
'touching your ears' is the definition.
(otic means relating to the ears)
'old idiosyncrasy' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'idiosyncrasy' becomes 'tic' (someone's tics are their idiosyncrasies or habits).
'o'+'tic'='OTIC'
'is' is the link.
(Other definitions for otic that I've seen before include "organ" , "of concern to the listener" , "of lugs" , "Relating to the ear" , "in relation to the listener" .)