Did what a tit does, and posted a comment online (7)
I believe the answer is:
tweeted
'did what a tit does and posted a' is the definition.
I can't judge whether this definition defines the answer.
'comment online' is the wordplay.
'comment' becomes 'tweet' (I've seen this before).
'online' becomes 'ed' (I can't justify this - if you can you should believe this answer much more).
'tweet'+'ed'='TWEETED'
Can you help me to learn more?
(Other definitions for tweeted that I've seen before include "Made a posting" , "used social media?" .)