With MJ, the black suit could change things too. If Peter becomes more confident in a cocky way because of the suit, MJ might not be as attracted to him. She might see him as a different person and start to pull away, which would make Peter realize he needs to get back to his old self.
Perhaps Spider - Man stumbles upon a hidden cache of vibranium. It could be in an old, forgotten laboratory or a secret vault. He then takes the vibranium and with his own knowledge of suit - making and some help from his friends in the science community, he constructs the vibranium suit.
It could enhance his senses. Maybe the suit has sensors that can detect things that his normal senses can't. For instance, it could detect hidden traps or enemies that are invisible to the naked eye. This would make him much more vigilant and better able to protect the city.
Well, if Spider - Man pooped in his suit, the story could start with his immediate reaction of shock and embarrassment. He might try to quickly web - swing away to a private place to deal with it. His friends or allies might notice something is off when they see him acting strange. This could lead to some humorous exchanges where they try to figure out what's wrong with him without him having to admit the truth.
One possible scenario could be that Spider - Man is in a really long and intense battle. He's been swinging around, fighting villains for hours. Suddenly, he gets a stomach ache. He tries to hold it in but as the fight gets more chaotic, he accidentally poops a little in his suit. It would be a really embarrassing situation for him and would add a comical and unexpected twist to the story.