"Well of course there's not! But I happen to be engaged, and engaged people don't just wander around asking their mates on dates." Okay, that may not be entirely true, but this is Donna, who to him is pretty much his sister. Or mother. Or...oh, there's that headache again.
"And no, I'm not bloody likely to involve Mister-High-and-Righteous-Who-Knows-Better-Than-Everyone-Including-Himself." He grins when she touches the console and the ship hums lightly in recognition. "No, no, just a social call. Wanted to give Rose the choice, of both worlds. Always did want to give her everything. And...I may have had a point to prove. To him." His face hardens just for a moment before the grin stretches across his face again. "Oh, Donna Noble, ready to save the universe again!" He jumps forward abruptly and wraps her in a hug. "I've missed you so much, you daft Earth girl."