Loaded, but ridiculous (4)
I believe the answer is:
rich
I believe this clue is a double definition.
'loaded' is the first definition.
(I've seen this before)
'ridiculous' is the second definition.
('that's rich' can mean 'that's ridiculous')
'but' is the link.
(Other definitions for rich that I've seen before include "Well to do" , "Possessing material wealth" , "Of great worth or quality" , "Deep - laughable" , "Full-flavoured" .)