Mug fools about, having drunk last of wine (5)
I believe the answer is:
stein
'mug' is the definition.
(stein is a kind of mug)
'fools about having drunk last of wine' is the wordplay.
'fools' becomes 'nits' (I've seen this in other clues**).
'about' shows that the letters should be reversed in order.
'having drunk' is an insertion indicator.
'last of' indicates one should take the final letters.
The final letter of 'wine' is 'e'.
'nits' back-to-front is 'stin'.
'stin' placed around 'e' is 'STEIN'.
(Other definitions for stein that I've seen before include "Large earthenware beer mug" , "German earthenware beer mug" , "Beer-mug" , "Inset (anag.)" , "Glass" .)