Specifically, it's 'The Christmas Invasion', the holiday special that was to serve as the bridge between the Ninth and Tenth incarnations of the Doctor before the 'Children In Need' charity telethon vignette came along.
I have yet to see this myself, but I expect to do so this coming week, thanks to my source(s) "Markhael". I would have done so already had it not been that they're enjoying themselves on the Brokeback Mountain Water Slide at Universal Studios Theme Park in Orlando, and as such are just a bit outside the range of my incredible mental powers.
But thanks to Brent, a TV blogging ally in the Great White North, I was able to verify the appropriate scene.
With each regeneration, the Doctor's personality quirks change along with his appearance, and that includes his taste in wardrobe. 'The Christmas Invasion' served as a bridge for that aspect between the two Doctors as well. For most of the special, the Doctor was out of commission and he spent all of that time in a pair of jammies.
When he finally became aware of his surroundings, the Doctor took note of his sleepwear fashion and said, "Ooh, very Arthur Dent."
'DOCTOR WHO: THE CHRISTMAS INVASION'
'THE HITCH-HIKER'S GUIDE TO THE GALAXY'
'THE HITCH-HIKER'S GUIDE TO THE GALAXY'
Well, of course, as a Time Lord, the Doctor would know of Dent, Arthur Dent. After all, it was through Arthur's inadvertent meddling in the Timestream which saved the Earth from destruction in 1981. In its original timeline, the Earth was vaporized by the Vogon Constructor Fleet to make way for a hyperspace bypass. But when Arthur Dent and his alien friend Ford Prefect were tossed back in Time to hitch a ride with the Golgafrinchans, they altered that projected history. The Golgafrinchans became Mankind's ancestors, not the pathetic cavemen who were native to this world.
(And apparently - according to the series of GEICO blipverts, - they're still around. And they're very touchy about their place in History.)
But the Doctor doesn't just know of Arthur Dent; apparently he actually knows him as well. In a quick aside to his companion, Rose Tyler, the Doctor adds, "Now there was a nice man."
I hope there's nothing untoward in the verbal past tense that was used.....
But it does mean that there's an unrecorded adventure out there in Toobworld that links 'Doctor Who' to 'The Hitch-Hiker's Guide To The Galaxy', which should quicken the pulse of fanfic writers everywhere.
Of course, we're talking about the TV version of 'Hitch-Hiker's', not the original radio drama, not the books, and certainly not the recent lump of cinematic excrement. This means the Doctor knew not only Simon Jones' interpretation of "Dent Arthur Dent", but also David Dixon's portrayal of Ford Prefect.
I always thought David Dixon would have made for a fine Doctor, as there was something of the Gallifreyan Twee about his performance as Ford. (That wardrobe of his went a long way towards this perception.) I realize it's been a quarter of a century since he assayed that role, and I haven't seen much of him since; but I think he would still be a good choice for future consideration to play the Doctor - very much in the Troughton mold.
(By the way, as I was watching the HHG2TG movie this past summer, squirming in my seat in tormented pain while doing so, I thought to myself that Bill Nighy was horribly miscast as Slartibartfast - but that he would have made for a damned fine Doctor!)
Because of the brevity in the onscreen career of Paul McGann as the Eighth incarnation of the Doctor, there is ample room for all possibilities in regard to his storylines. So I think it would be the Eighth Doctor who more than likely encountered Arthur Dent.
But I'd love to see David Dixon as Ford meeting David Tennant as the Tenth Doctor.
And for good measure, I'd like to see the programmed personality of Marvin the Paranoid Android downloaded out of the televersion of his robotic body and into the cinematic cybernetics as manipulated by Warwick Davis. That was the only good thing to come of the movie.