Believe I remember reading in Scott O'Grady's book that the pull handle in the F-16 required 35lbs of pressure, which he considered to be a lot, but how easy he found it to pull when the time actually came. That I think is the ACES II system, where the Rafale is an MB MK16 one. I would guess the pressures are pretty universal.
There's a little light reading about ejection seats, though no specs on the pull pressure required. Also has a ton of info. Little clunky to navigate, but good.
As to how a civilian could pull a handle accidentally... I guess throw someone into a jet, pull a half dozen Gs and watch them grab for something. Most tandem aircraft have split ejection "options", for lack of a better term, meaning the RIO/FO/passenger can punch himself out, but leave the pilot inside. Gotta be a hell of a surprise when the back seater disappears like that.
Likewise, I've seen and heard of numerous cases of canopies being blown accidentally without an actual ejection. Had an F-15C I was working on do it one afternoon in FL.