Concerning short trousers and flashy jewellery (9)

'concerning' is the definition.
Although both the answer and definition are present participle verbs, I cannot understand how they can define each other.

'short trousers and flashy jewellery' is the wordplay.
'short' suggests taking the first letters.
'and' says to put letters next to each other.
'flashy' becomes 'rou' (I can't justify this - if you can you should believe this answer much more).
'jewellery' becomes 'bling' (informal term for jewellery).
The initial letter of 'trousers' is 't'.
't'+'rou'+'bling'='TROUBLING'

Can you help me to learn more?