I'll ruin toast? Bad example! (12)
I believe the answer is:
illustration
'example' is the definition.
('illustration' can be a synonym of 'example')
'i'll ruin toast? bad' is the wordplay.
'bad' is an anagram indicator.
'ruin'+'toast'='ruintoast'
'ruintoast' with letters rearranged gives 'ustration'.
'ill'+'ustration'='ILLUSTRATION'
(Other definitions for illustration that I've seen before include "Picture in a book or periodical" , "Drawing - example" , "plate" , "Sample" , "Picture; example" .)