Son trying bad language (8)
I believe the answer is:
swearing
'bad language' is the definition.
(I've seen this before)
'son trying' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'trying' becomes 'wearing' (both can mean stressful or demanding).
's'+'wearing'='SWEARING'
(Other definitions for swearing that I've seen before include "Foul language" , "Vowing" , "Affirming or cursing" , "promising" , "Expressing annoyance" .)