Why did Whiplash say "you lose" in Iron man 2?

Why did Whiplash say “you lose” in Iron man 2?

This comment has to do with Whiplash's overall goal w.r.t. Iron Man, which is to puncture Iron Man's reputation and credibility, from the aspect that -- Tony Stark claims Iron Man technology won't be mainstream for another 5-10 years.. by Ivan Vanko developing a weapon that utilizes arc reactor technology, he's demonstrating that such a threat is possible now, and not several years down the road.

From the conversation with Tony and Whiplash just after the Monaco scene:

TONY: The reason I’m alive is ‘cause you had a shot, you took it, you missed.

IVAN: Did I? If you can make God bleed, the people will cease to believe in him. And there will be blood in the water. And the sharks will come. The truth, all I have to do is sit here and watch as the world will consume you.

And then, when Hammer first speaks with Whiplash in the hangar:

JUSTIN: But if I might make a suggestion, you know, you don’t just go and try to kill the guy. I think, if I may, you go after his legacy. That’s what you kill.

Or did he know that Pepper Potts is near one of his exploding drones and hence consider killing Tony Stark's lover a "lose" for him?

Ivan fought the majority of the fight with his helmet off, and, at the time of him saying "you lose" to Tony, his suit was completely destroyed. That being said, Ivan would have no way of knowing that Pepper was near a drone that was about to explode.

Only unless perhaps Ivan had programmed one of the drones to follow Pepper around and be near her on the off-chance that he dies, would Ivan have known that Pepper was about to die. Other than that, I don't see how Ivan would know both the whereabouts of Pepper, and the fact that she's nearby a drone that's about to explode.

This doesn't seem to be the case though, since the drone was destroyed and laying on the steps, and Pepper appears to of coincidentally walked up on it.

FWIW, Whiplash actually first mentions Tony "losing" just after their fight at the Monaco Grand Prix:

The Self-destruct was Vanko's last desperate move, and he expected it to work

As has been pointed out in other answers, Vanko's motives early in the movie do not require him to kill Tony Stark or even to beat him in combat.

STARK: The reason I’m alive is ‘cause you had a shot, you took it, you missed.

VANKO: Did I? If you can make God bleed, the people will cease to believe in him. And there will be blood in the water. And the sharks will come. The truth, all I have to do is sit here and watch as the world will consume you.

Vanko has a preoccupation with having the last word, and mocking Stark whenever it seems Stark has beaten him.

After the fight at the racetrack, he laughs, spits and shouts at Stark:

VANKO: You lose, Stark! You lose!

His parting shot to Tony after their conversation in Vanko's cell:

VANKO: Hey Tony, before you go? Palladium in chest…painful way to die.

However by the time of the final battle, Vanko is no longer content to let matters take their natural course; with Hammer's backing he has the resources to overwhelm and destroy Stark, not merely wound or embarrass him. It could not be forseen that Stark (aided eventually by Rhodes) would be able to defeat the Hammer drones AND Vanko. Nonetheless, Vanko's self-destruct was put in place as a final sting if he were defeated.

There is no deeper meaning than the one you suggest - Vanko's self-destruct was intended to hurt or kill Stark. Vanko allows Stark and Rhodes to approach before delivering, in his usual style, the 'last word':

VANKO: You lose.

There can be no other meaning, as Stark's prosperity at the end of the movie indicates that he did not lose.