Sneaky

Have any of you guys ever came into girls drink without her knowing or anything like that. But I'm almost positive I caught one of my friends doing it to me I don't really know when it started but we hang a lot the most recent time he had gotton coffee and we were at my house and I left the room for a min when I came back in he was like startled and his fly was undone then it kinda made sense cuz I noticed sometimes my drinks tasted diff I don't what to say I drank most of the coffee because I didn't want look obvious Anything?