Yankee wears large pants and small socks (7)

'socks' is the definition.
(I know this)

'yankee wears large pants and small' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'wears' indicates putting letters inside.
'pants' indicates an anagram (UK informal term for 'nonsense' or 'rubbish').
'and' is a charade indicator (letters next to each other).
'small' becomes 's' (abbreviation - e.g. clothes size).
'large' is an anagram of 'argle'.
'y' inserted into 'argle' is 'argyle'.
'argyle'+'s'='ARGYLES'