The claim here is that B12 only is created by bacteria in the soil or in manure. Self-identified "anti-vegans" will claim, for sarcasm or weak shock value, that therefore "the only way to be vegan without fortified foods or supplements is to eat shit".
Did you know that 100% of ground beef (at least in western countries) contains bacteria consistent with fecal contamination? Not to mention all milk has some quantity of somatic cells (a.k.a. pus) in it, with really high allowable quantities.
So in the shit-eating department it's funny to claim that vegans would have to consume feces (if only reality were different), something which carnists actually do every day.