Just... O.K.? is something Barney says when he is either caught lying or nobody wants to do the same thing he wants.
When Barney has The Yips and Heidi Klum gives him advice and he leans in to kiss her. She walks away, then he claims to have made out with her.
After getting caught in a lie by a woman he had already had sex with and one he was going to, Barney claims to have resolved it with “the best threeway ever”. Ted and Marshall realise he’s lying. - Zoo or False
Barney caught lying about the Dutch ambassador when told that the ambassador was a woman - Robots Versus Wrestlers.
John Clifford Larrabee, who looks like Barney, appeared in Ted's dream and tries to convince Ted that it's a dream - Landmarks.
Barney insisting on Ted wearing a brobe during The Broath - The Broath.
Barney guiding Ted with one of his Playbook plays when Ted complains about the play being ridiculous (Barney says: "...just... ok, over? Ok, over?" because he was talking through the radio". - Weekend at Barney's.
Barney wants to talk to Ted through his Jor-El cam in The Fortress.
Ted uses the phrase in Ducky Tie, when Robin reveals he didn't act as cool as he claims when running into Victoria.
Barney also uses this pharse in a meaning of just go with it or, stop ruining this.