Update: The poll has now received over 200 votes!!
Therefore as a thank you, I will add 2 additional dares (that I REALLY don't want to do!) in case we reach 300 or 400 votes.
300: Insert a laxative suppository and wear a diaper - go outside for 10 mins * dice roll - which means if I get 2-3 or higher I will likely shit myself outside, and still can't return home until the timer is up, even if it stinks/leaks 
I've always been curious about this but it would be super gross and I've never done anything like it before as it potentially combines two limits of scat and non-discrete public...
400: When I do the bath of piss, I will take an enema of piss and expel it into the water. I will also vomit into the bath (let me know if you want a vomit enema too?!). I'll tie myself up in the bath, stay there for at least 1 hour (instead of 30 min originally planned) AND will dunk my head under the water AND will stuff shit up my nose so it's all I can smell... Wow this one would be awful (but at least noone else can see me!) and would need so much tidying up afterwards..! And as I can't wash I would stink of shit!! 
Finally, as mentioned in my original post, if the poll hits 500 votes then I would strip fully outside - plus will stuff shit up my nose under my mask! This is a huge limit, as there aren't many places nearby where I could do this at all discretely...! 
Thanks again for everyone who voted! Please keep it up and feel free to suggest additional dares in this thread!