Over a year ago, I had an issue with my players killing without remorse and being general scumbags. Back then, when I asked for help, someone told me my players were "Murderhobos." The situation was resolved, but now it's arisen again with the start of a new campaign. I don't know for sure what the cause for sudden change is, specifically with my primary player who's generally very serious, but it's a serious problem. So the question is, what should I do to fix the problem? I know that one of the players is generally less serious but still not terrible, while a new player spends half the time making up joke scenarios and the other half arguing why he should be able to do things such as cut through walls and carry two backpacks.
Any advice will be very appreciated. Thanks in advance.