Haven't read the OOC post yet as of this writing, which I'll get to after. Originally in my SU, I really wanted to get across that everything Jasper was taught, included the prejudice terms that specifically Malfoy or Bellatrix had used in the book. I ended up leaving things vague though, cause in my last two SU's, I kinda wrote everything in character, and the GM got confused.
Those specific terms would be "Mudblood" and "Filthy little Half-Blood" respectfully, which I basically wanted to associate with today's idea of how those words would be considered nothing more than swears in our world, meaning Jasper would look odd to other Slytherins for suddenly freezing in place of what he usually says.
Of course, if it's not enough, then like you have suggested to some of the SU's, perhaps the curse would make him replace these terms with something like a compliment? Poking fun at the idea of a stumbling Slytherin is really what I'm going for here with the curse.