If you want to have a little fun with your friends follow me.
Step 1: What You Need
To do this prank you need a mechanical pen.
And also you need your friend's eraser; you can borrow it.
Step 2: One Easy Step
Embed the lead of your mechanical pen into the eraser corners.
Step 3: What Will Happens
Now when your friend is going to erase paper with eraser, he/she can't erase it clearly.