Holidaymaker's complaint? Not all pick up litter! (4,4)
I believe the answer is:
heat rash
'holidaymaker's complaint?' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'not all pick up litter' is the wordplay.
'not all pick' becomes 'aeh' (I am not sure about this - if you are sure you should believe this answer much more).
'up' is a reversal indicator (in down clue: letters go upwards).
'litter' becomes 'trash' (I've seen this in another clue).
'aeh' written backwards gives 'hea'.
'hea'+'trash'='HEAT RASH'
Can you help me to learn more?
(Other definitions for heat rash that I've seen before include "Irritating inflammation of sweat glands" , "Itching of the skin, caused by humid hot weather" , "skin complaint" .)