Tiny boy turning up, looking embarrassed, wearing a special hat (6)

'wearing a special hat' is the definition.
(a mitre is a bishop's hat)

'tiny boy turning up looking embarrassed' is the wordplay.
'tiny boy' becomes 'tim' (A Christmas Carol character Tiny Tim).
'turning up' says the letters should be written backwards.
'looking embarrassed' becomes 'red' (I've seen this before).
'tim' in reverse letter order is 'mit'.
'mit'+'red'='MITRED'