Robert Herjavec, Kym Johnson -- Kiss, but Don't Tell

"Shark Tank" star Robert Herjavec has an interesting way of saying goodbye to his "friends" ... by planting a big, juicy wet one on their smackers.

Robert and his "Dancing with the Stars" partner Kym Johnson were leaving Greenblatt's Deli in Hollywood Friday night, where they were full-on kissing.

A coy Robert explains, they're not dating ... they're just friends who dance.

They've actually been very open about their relationship ... people on DWTS all know the deal.