Two brilliant Indian research students Indrajeet Bhuyan and Saurav Kar, have demonstrated that you can crash your recipient's whatsapp by sending a message with just 2,000 special character.
What actually happens is that Whatsapp in its coding presumes that a message will contain less than 2000 special characters. But as a matter of fact, 2000+ character weigh more than 2KB of data crashing the recipient's whatsapp.
The recipient have to delete the entire conversation otherwise the app will keep on closing by itself (as shown in the video). This could be a bad joke for your friends but if you wish to delete your entire conversation with an annoying person, just send him something special in his/her textbox .
If you have Whatsapp version '2.11.431 and 2.11.432' then this may affect you. Also this whole thing seems effective with Android versions up to 4.4.
Kindly note that it was first reported by 'The Hacker News'.