1. Literally, to attempt to move past someone or something without being seen or detected. The spy used a disguise to sneak past the guards.

2. To transport someone or something past some guard, inspector, checkpoint, etc., in a surreptitious, deceitful, or stealthy manner, especially when it is illegal or forbidden to do so. In this usage, a noun or pronoun can be used between "sneak" and "in." I tried sneaking a bunch of Chinese snacks past customs and immigration when I flew back into Sydney Airport, but they caught me and made me throw them all away. My cousins tried to sneak me past the bouncer, even though I was only 18.

3. To cause something that is normally forbidden, unwanted, or frowned upon to be accepted or go unnoticed by someone or something through sly, subtle, or surreptitious means. In this usage, a noun or pronoun can be used between "sneak" and "in." The writers of the popular kids' show were always trying to sneak adult content past the network censors. The senators have been accused of trying to sneak unrelated spending increases past the rest of congress by hiding them inside the recent healthcare legislation.