Well, I don't think it needs to be ranked up there with malicious and/or evil behavior. You don't even need to put anger in there.
Just make sure he understands that HE is doing the cleaning. HE picks it up. HE puts it in the toilet. HE gets the germicide and sprays it. He scrubs the carpet or whatever. HE will wash his underwear (to the best of HIS ability) by hand and then take it to the wash machine.
So long as he understands there's follow-up to any choice he makes. You cannot make him be disgusted by something you are but you can make sure he cleans up his messes.
I also want you to understand that this could be something more that just laziness or something nice like that. He could be telling you something is wrong in his world. It's best you pay special attention to your son's life: interactions, new people (including--and especially--babies), lack of interaction with someone he's bonded to (like you if you've picked up a job, added hours, have a new hobby, etc...or Dad if dad has to travel now, any other person). It isn't all that unusual for young ones to revert if they feel stressed or there's another child they feel is getting more attention by not being potty trained...it isn't so much being naughty as being wrong in their assumption of how to get attention they feel they're missing. KWIM? If you're just certain NOTHING is amiss AFTER a complete and thorough inventory of his world and interactions, talk to your son's care provider to rule any physical problems.
If everything turns out just splendidly perfect then you'll just have to help him not have accidents by keeping him with you at all times until he's able to control himself again which means he can't play or watch movies/tv unless that's what YOU'RE doing. This will get really old, really fast. You have to be overly dramatic about it, never leaving a room without him and having an over-the-top "concern" in your voice. It works if you're committed and able to be patient to attain a goal. (don't get me wrong; I'd totally understand if you found it difficult to be patient with poop on the floor!) BUT once you bring anger and power into it = you both lose!!!