Don’t take your harp to the party

Don’t keep on talking about the same thing or bringing up the same subject. Literally ‘to harp’ is to play the harp; figuratively ‘to harp on’ is to dwell tediously on a matter.

See also:

• Harp not for ever on the same string
• It is useless to flog a dead horse
• Not good is it to harp on the frayed string