National Handshake Day is trending on twitter today ( on Thursday June 28th 2018 ) because its celebrated on the Last Thursday of June every year! :) 

*So HAPPY NATIONAL HANDSHAKE DAY, My Friends!  ^_^ 

*Don't worry if You Haven't Heard about This Holiday before! 😊

- Cause You can Shake My Hand & Celebrate!  ^_^ 

*( Sounds like some Trolls Holiday, doesn't it?  ^_~ )