a cat that provides as
forensic evidence against you, thereby putting you in jail, can do you in. (google search "your cat may do you in")
high heel shoes that will cause health problems down the line may do you in. (google search "These heels might
just do you in")
"I'm gonna do you in" could mean "I'm going to beat you up". (This has a totally different meaning than "I'm gonna do you". "To do" someone can mean to fuck them, in Southern California terms at least, but also see this: to+do+you )