How do you tell others (or prefer to be told) that the zipper is not...erm...engaged
Well it depends on who it is. If it's a guy who I am comfortable and who I know is aware of my sexuality and the fact that I do not see thme as an object of desire, I will make rather lewd remarks. My usual in that case is along the lines of I had no idea you wanted me so much that you couldn't wait to get home! and then wriggle my eyebrows in as sexy a way as I can. However with most men I just lean over and whisper soft that their zipper is down.
As to someone letting me know, I don't care how it gets done as long as it does.