In the end, of course, he would blame Donna. Because it was clearly her fault.
Oh, no, it couldn't just be a simple series of trips and adventures, could it? No, a few adventures and then suddenly she wanted to be taken somewhere where she could get alcohol she'd never tried before. In space.
"All of time and space at your disposal and you just want me to find you an intergalactic bar??"
"Oh, come on," Donna had said. "All of time and space and you haven't found one yet?"
Well, the Doctor had traveled with Jack for a while. His intergalactic rolodex was full of a variety of space bars (and phone numbers for women and men Jack had picked up there). Well, he wasn't one to deny Donna a little fun (and she really was old enough to make her own decisions on alcoholic intake), so he set the coordinates.
"I don't know if your metabolism could handle some of the drinks out there, Donna. Are you sure you want to try?"
"I'll judge that one myself. Always have been good at figuring out how many drinks before I need a breather."
So, the next thing the Doctor really could recollect, he and Donna were slouched over a table, with a wide variety of strangely-shaped shotglasses around them. With typical ethyl alcohol the Doctor could control his metabolism and keep himself from getting drunk. With hypervodka? Well, he was finding himself rather pleasantly pissed.
He tilted his head. "Are you sure this was a good idea, Donna?"