You can change the profile picture of one of your contacts in your smartphone.
A good joke for friends.
How to Change Friend’s Profile Picture on Whatsapp
You would need to have a photo, resize it to 561 × 561 and name it with your friend’s number,
Then save it in SD card> WhatsApp > Profile Pictures, overwrite the previous one if it already exists.
Now turn off the internet connection (mobile data or Wifi) then in WhatsApp, your friend’s profile picture will change automatically.
Now you can show it to your friends and they will be surprised.
Once the internet connection is reestablished, the real photo will overwrite the false one.
See as well : Here is how to use Whatsapp without a SIM card in your phone