。
Don't meddle in my affairs.
Literal
I [of-の] matters [in-に] don't-interfere [give-くれ].
干渉する ('to interfere, to meddle') is a formal noun+する verb. に marks the target of interference. 僕のこと ('my matters, things about me') uses こと as the general 'stuff about me.' A direct refusal of unwanted involvement.