Q: is rubbing alcohol safe to clean my trackpad or my screen? can beer or watermelon juice damage your laptop?

isoproply alcohol (rubbing alcohol) is certainly a big NO on the screen.  Any liquid can easily damage the laptop or any laptop, yes.

Keep your macbook away from water regardless. The casing and the screen, if dirty, can receive only a VERY SLIGHTLY DAMP cloth to remove dirt.

Those who have used a wet rag/cloth on same have encountered damaging their macbook resultantly.

very slightly damp = twisting the cloth extremely tight and not even a drop of liquid comes out

Why, did you spill water into your trackpad?

Read the cleaning instructions that in the user manual that came with your computer.