The highest I ever got in a glider was 20,300 feet agl, over Aboyne on the River Dee, in Scotland. The height record there was set with Chris Rollings and Briony Hicks in a 2 seater, somewhere around 38,000 feet, I think. But the highest one of course was in the US, c. 48,000.
Tis said that he had oxygen, under pressure, but the veins in his legs squirmed like worms. And the FAA was none too pleased, as one doesn't always know when it is the perfect day, he hadn't authorised his special VFR above 18,500, as one was supposed to do. Don't know whether or not he was wearing shorts.
We in gliders do definitely enjoy looking down on airliners, but usually are talking to enroute controllers, or have a special window of space opened for us. One glider pilot of ancient fame used to soar his Auster (a primitive SEP, rather a shed, actually) up to 20,000 or so. The controller, when receiving his transmission, had to ask several times "What type aircraft did you say?!"
Pace, I'm sending you a private message.