be in a rut	be stuck in a monotonous routine
off the record	unofficially
hit the roof	get very angry
put down roots	settle down
work to rule	adhere strictly to the regulations as a form of protest
it stands to reason	it is logical
as a last resort	when all else has failed
know the ropes	know all the details of sth
in the long run	after a long period of time
rock your brains	think very hard about sth
on the quiet	secretly
cut sb to the quick	deeply hurts sb’s feelings
open to debate	undecided/unsettled
an unknown quantity	person or thing that one has no experience of
at close quarters	from a short distance
sth begs the question	makes ppl want to ask a particular question
call it quits	give up/stop
out of the question	impossible
be in a quandary	be confused; undecided
keep sth quiet	keep sth secret