Yankee breaking thousand hearts regularly? Nonsense (2,3)
I believe the answer is:
my hat
'nonsense' is the definition.
(I've seen this before)
'yankee breaking thousand hearts regularly?' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'breaking' indicates putting letters inside.
'thousand' becomes 'm' (Roman numeral for a thousand).
'regularly?' indicates alternate letters (I've seen 'regularly' mean this (regularly take one letter, leave next etc.)).
The alternating letters of 'hearts' are 'hat'.
'm'+'hat'='mhat'
'y' put into 'mhat' is 'MY HAT'.
(Other definitions for my hat that I've seen before include "Exclamation of surprise" , "stuff!" , "nonsense" , "Old-fashioned exclamation" , "Out of respect I might remove this" .)