How do you skip prom together properly?

@darkaudit   Hi!  You didn't miss anything.  Unfortunately, this is by design and, in my opinion, a design flaw.  Whether or not your sim goes to prom, if they have romantic interest with another sim (or sims) they will get the "no prom invite" sentiments if your sims were not invited to the prom by their romantic interest(s) and the NPC sims will get the same sentiments if there is no invite.  I don't work for EA and I'm not saying this is how it should be.  Again, I think this is a design flaw that should be corrected.

Edit: Even if you decided to go to prom and invited one of your sims' romantic interests, if your sim has more than one romantic interest then they will get a "no prom invite" sentiment towards those other sims.  It's ridiculous really.

I just noticed this too. I made it into a storyline where my sim broke up with his girlfriend because she got pissed off about no prom invite even after they promised to skip prom. But it would be nice if this was actually reflected in the sentiments. Especially since your sim gets resentful too and unless you control the other sim, it's unlikely they'll apologize. I usually love the sentiments, but there are nuances in certain interations that the game doesn't take into account for sentiments even if these nuances are actually coded into the game (eg. the neighbourhood brawl being a friendly interaction)