My favorite SSSS experience happened some years back. I was flying from Tampa to Seattle, with a change of planes in Dallas. Weather in Dallas was very bad, so the AA gate agent told me that I was going to miss the last flight out of Dallas to Seattle. I fired up my computer, found an alternate flight via USAir that would avoid the night's stay, and got her to send me to the USAir check-in desk with a voucher.
That's where things got a bit dicey. The gate agent seemed a bit harried--I think bad weather across the Midwest had made for a frustrating day for a lot of passengers. She quickly took my voucher and issued me a boarding pass--middle seat in the back of the plane. I asked if my USAir frequent flyer number was in the system and she snapped "Just send in your boarding pass stub after the flight." Well, as a USAir Gold (at the time) I thought that perhaps I could get a little better seat assignment as well as avoid the hassle of sending my stub in for the mileage, so I asked her to please re-issue the boarding pass with my number and to check if there was a better seat.
You will have to take my word for it that it wasn't with a DYKWIA kind of attitude--I'm by nature pretty diffident, actually. But, probably since she'd had a bad day, she made a big show of rolling her eyes, sighing really loudly, ripping up my old boarding pass into pieces, and handing me a new boarding pass (which was, as it turned out, in the front of the plane, aisle seat!) It also had on it SSSS.
Took it to the checkpoint, where I was whisked off to a private room for a SSSS special patdown. (This was long before the current prison-style patdowns.) I told the screener why I had been given the special designation, and got the world's most perfunctory patdown and an apology from her. She strongly recommended that I complain to US Air about a gate agent using the SSSS designation for petty retaliation.
So, I did. To my surprise, I got an actual letter back from Customer Service, apologizing for the rudeness and inappropriate behavior of the gate agent, who they said they were able to identify from my description. Got a $200 voucher and 10,000 extra miles as well.