Possible broken motor mount. This is where the engine sits on a rubber support which is mounted to the frame of the car.
If it's just a minor shake, like a buzz that wasn't there before your friend screwed around, you might have a broken engine mount or transmission mount. These include little rubber cushions that typically isolate that vibration, but if they're broken the vibration can translate into the car's cabin as a buzz/rattle/groan noise.
If the car shakes while you are braking , it is likely the rotors are warped. If it is after the car has stopped already, then it is something else.
P.S. you need a new friend
Check your spark plug wires make sure there not touching your engine
Carb. or injectors? The carb. may need tuning a little.
OK my car is exactly 102200 miles. Knowing I need new brakes and rotors. But thing that has started now is that when I'm in break (in stop like at a light etc.) the car starts to shake. I can feel it more in the driver's seat. Also it kind started after my friend was being stupid and put the car in park while I was driving, but only for a few seconds. Some people say it maybe the transmission like a loose gear or damaged gear, but I'm not sure. What is causing the shaking and what might be the cost of it???? Please let me know