From Wiktionary, the free dictionary
IYSS (not comparable)
- (Internet slang) Initialism of if you say so.
2001, Owl, “Domi”, in alt.sports.hockey.nhl.tor-mapleleafs (Usenet):IYSS. I took that to be part of the whole deal with cheap-shot artists hoo[sic] take it out with elbows and butt-ends.
2001, zeldabee, “Sharpest kitchen knife [long]”, in alt.2eggs.sausage.beans.tomatoes.2toast.largetea.cheerslove (Usenet):> Odd, that, isn't it, how "traditional" and "best" are so ofthen [sic]
> found together! Shows us something, I suppose.
IYSS