Davis Clarke says he had a crappy run at the Boston Marathon, and he seems to mean that literally -- claiming he crapped his pants ... but TBH, take it with a grain of poopy salt. The TikTok star/influencer filmed himself crossing the finish line Monday during the annual race in Beantown -- and he says he s*** himself ... proving just how damn dedicated he was to the cause. The camera does capture what looks to be blood running down his legs. It's definitely a gross sight ... and by the looks of it, it wasn't just a little accident either -- assuming this is actually real, which we're not so sure it is. Fact is ... this dude is a bit of a troll, and his whole grind-set schtick is basically him leaning into being a motivational bro for his followers -- so this whole thing is likely just a gag. Still, if it is ... he definitely committed to the bit. Anyway ... Davis was certainly proud of himself for accomplishing the feat -- and he threw up some extra social media posts to ring in the momentous occasion ... hamming up his internet personality for the camera. Like we said ... can't tell if the dude actually crapped his pants or not -- but if he did ... props, we suppose. And, if he didn't ... props for that too for making everyone buy it. Can't say the guy isn't devoted.