As a teenager she would 'sneak' out (of her house/apartment) at night to visit her boyfriend.
I'm going to 'sneak' a smoke. [=I'm going to smoke a cigarette while nobody is watching]
She took a 'sneak peek' [=a secret look] at the birthday presents hidden in the closet.
(..) So anyway, one night she plays it real cool. She waits for him to get drunk. He falls asleep on the fuckin' couch. She sneaks up on him, puts some glue on his dick... and glues his dick to his belly. Jesus Christ! I'm serious, man. (..)1992 Reservoir Dogs