Get lost in rhythm with no boundaries (4,2)
I believe the answer is:
beat it
'get lost' is the definition.
(both can be used to tell someone to go away)
'in rhythm with no boundaries' is the wordplay.
'in' is an insertion indicator.
'rhythm' becomes 'beat' (synonyms).
'with no boundaries' becomes 'ti' (I can't explain this - if you can you should believe this answer much more).
'beat' going around 'ti' is 'BEAT IT'.
Can you help me to learn more?
(Other definitions for beat it that I've seen before include "Sling your hook!" , "Get going" , "Clear off!" , "make off furtively" , "leave" .)