At least if a guy looks even a bit like a barbarian, then nobody pays any attention to any amount of naked skin (within obvious limits). Grimmjow falls well enough within that definition. Sai does look too sophisticated to have any outwardly evident barbarism in him.

Well, I personally think one short scene is quite little to make any definite judgements on what kind of impression he will ultimately leave. I mean, if he turns out to be another ero-ninja who continuously sexually harasses Sakura and other female ninjas, it would be kind of hard to keep thinking he swings towards his own sex...