Full House - Season 7 Episode 10 : The Prying Game 1995

While at a local public library, Stephanie sees an attractive blonde haired girl planting a kiss on Steve's cheek. Stephanie doesn't want to say anything to D.J. until she's sure Steve is seeing another girl. That's why Stephanie and Kimmy break into Steve's apartment, so they can investigate. Stephanie and Kimmy are nailed when D.J. and Steve show up. The girl who kissed Steve on the cheek was his cousin Edie, who kissed him out of friendship, proving that Steve is not seeing someone else. D.J. goes ballistic and tells a stunned Stephanie to stay out of her life, because D.J. feels that by breaking into Steve's apartment, Stephanie has reached a new low when it comes to invading D.J.'s privacy.