Personally, I’d think not, as long as the word is used to literally identify when someone has a brown skid mark on the rear end of their clothing and/or underwear.

Now if I used it as an insult and called you or someone else a shart, well yeah I think it would be interpreted as offensive.

To me, it’s all in the intent of the word. But then again, I don’t give a flying fuck. Hell, I can’t even fly to save my own damn life. Shit.