Only say this on the internet or texting. If you want to say it in real life, say "Haha. Just kidding. . but seriously though".
*It can be reduced to: LOL jk but seriously
Lily: Dude, Sally needs to stop making out with everyone.
Mary: I know right! She's such a whore. LOL jk but seriously though.
(John is driving his girlfriend's bug)
Bill: Hey, John, can you give me a ride?
John: Sure, man!
(they walk to John's car)
Bill: Whoa. Dude, that is one fruity car. Haha just kidding. . .but seriously though.
John:. . . that's my girlfriends car. .