Australian males drinking head of lager make silly mistakes (8)
I believe the answer is:
bloomers
'silly mistakes' is the definition.
'australian males drinking head of lager' is the wordplay.
'australian males' becomes 'boomers' (informal term for male kangaroos).
'drinking' means one lot of letters goes inside another.
'head of' suggests taking the first letters.
The first letter of 'lager' is 'l'.
'boomers' placed around 'l' is 'BLOOMERS'.
'make' is the link.
(Other definitions for bloomers that I've seen before include "made by clothing manufacturers" , "Undergarments popularised by Amelia" , "Flora" , "Embarrassing mistakes" , "Slips" .)