Green’s Dictionary of Slang

to eavesdrop, to butt into another’s conversation, to pay more attention to other people’s business than to one’s own.

1970		Current Sl. V:2 7: Dip, v. To meddle.
1981		Eble Campus Sl. Fall 3: dip – to meddle, be nosey.
1995		Eble Campus Sl. Dec. 2: dip – be nosey, get into someone else’s business: ‘Why you dippin’ in our conversation?’.