Right in a mess? That's tough (5)
I believe the answer is:
harsh
'tough' is the definition.
(thesaurus)
'right in a mess?' is the wordplay.
'right' becomes 'r' (common abbreviation).
'in' is an insertion indicator.
'a mess?' becomes 'hash' (I've seen this before).
'r' inserted inside 'hash' is 'HARSH'.
'that's' is the link.
(Other definitions for harsh that I've seen before include "Strident" , "Unpleasantly stern" , "Jarring" , "Severe - unkind" , "'Severe, rough (5)'" .)