You must have observed this feature on Facebook. Facebook Poke is an old feature of Facebook. Now you can enable Poke in your BuddyPress site too. BuddyPress Poke is the new plugin by Anu Sharma. The plugin simply activates Poke in BuddyPress that enables your community members to poke other members, just like Facebook.
Other user profile
Poke screen
Error message
Poke back screen
Simply install and activate the plugin. Upon activate your logged in members will be able to poke by visiting other users profile and using poke button.