First of all, I still don't condone giving dirty looks or rude comments to people in the FP line from people in the SB line but another scenario which hasn't been mentioned is that maybe they DO in fact know how to use FP they just weren't able to get one.
On my last trip we park hopped so often hit some parks in the afternoon and found a few rides (TSMM, PP, Splash, EE, ToT, RnR, Soarin, TT and probably others) ran out of Fastpasses by the time we got there.
So maybe the dirty looks aren't from people who have no idea how to use it but were upset that by noon they were all gone and they weren't able to get any.
Also, for the few people who responded when I said that I knew people having their first trip and didn't know wll the ropes and was told they should have done research, while I agree that research should be done to help the trip go smoothly, I would hope that Disney fans would allow for some margin of learning about things while at the parks.
I certainly don't expect everyone to know within the first hour of arrival how and when to get FP's and which rides will need them first, which restaurants need ADR's and which part of the DP they fall under, which entertainment can be cxl'd due to weather, which mornings and nights are EMH, which parks are busiest on what days and hours etc etc etc. They may have looked into all of this but not have memorized every bit so there will be a little confusion until they access the proper info.
The people I know that have returned from their trips all managed to use FP once they got there and I must admit, they were given incorrect information by CM's ... one was told that no more TT FP were being given out for the day and got to TT to find out they were still available. Another family was told at AK they could only get one FP at a time and this was when the FP island was set up and they managed to get 4 FP's at the same time for the family.
I'm leaning towards giving people the benefit of the doubt. I never noticed one dirty look in all the FP's I used on my last trip so I never experienced what other people have but I know I had to wait in some lines I wish I had FP's for but wasn't able to so while I may have looked tired, I hope no one thought I was giving them dirty looks.