Do you see Jack or Sally ever getting jealous if anyone tried to make advances on either of them/ especially if someone already knew they were together?
Whenever I think about jealous!Sally and jealous!Jack, I tend to think of some of the Disneyland videos where guests flirt with them, where the results can be a little different. Of course, there's the video where someone straight-up proposes to Sally, making Jack walk off VERY stressed-like, and comes back relieved when she says 'no'. LOL.
I saw someone on deviantART who got away with giving Jack a kiss on the cheek; Sally wasn't there at the time, so I don't know how that reaction would've gone down, but we can use our imaginations..! In one of BriannaCherryGarcia's videos, I remember a guy posed with Sally for a picture, and Jack noticed he was using HIS pose and adamantly told him to change how he was standing, LOL. And in another video, Sally was talking about plans she had with a 'friend' in Valentine's Town, and Jack got quite suspicious of that.
These are little reactions/details from the Disneyland actors that I have closest to how Jack and Sally would act if they were jealous. But in the movie-verse, I think she's used to seeing Jack getting admired and complimented/flirted with by the citizens every Halloween, so it's nothing really new to her, as much as she may not like it. But I like to think he puts more boundaries with that as soon as he's openly courting Sally, which puts her discomforts at ease.
As for seeing someone infatuated with Sally, I think it gets more on Jack's nerves than he credits himself for, and he tends to react very strongly when he sees it happening. They both have faith in each other and when they're married, I don't see a huge cause of concern for jealousy, buuuuut I think it does happen from time-to-time, when anyone's bold enough to do it in front of the other. :P