First thing you gotta do, is find an old gardening, sports, or construction tool that no one uses anymore, e.g., a shovel, baseball bat, lead pipe, etc.
Then you gotta make it look more shitty than it already is by wrapping tape and or strings around it.
After that, you gotta put some DIY mods on it to make it do more damage. For example, you can put some spikes on your bat or put a bunch of rocks in an old pipe to make it heavier.
Once no one suspects the weapon of choice, you can take out your target, but do it this exact way: Follow them, tap them on the shoulder, then when they look back, knock them out by hitting them as hard as you can with your fist and or the club.