Jokes about a couple of heartless hoaxes (3-3)

'hoaxes' is the definition.
('put-on' can be a synonym of 'hoax')

'jokes about a couple of heartless' is the wordplay.
'jokes' becomes 'puns' (punning is a kind of joking).
'about' is an insertion indicator.
'a couple' becomes 'two' (a couple can mean two of something).
'of heartless' means to remove the middle letters (I've seen 'heartless' mean this).
'two' with its centre removed is 'to'.
'puns' placed around 'to' is 'PUT-ONS'.