The "phasing out of conversations" thing has been mentioned a few times, although I usually try to cover it as well as I can by trying to guess whether they made a joke, or said something serious, and either laughing or making an appropriate "hmm" noise , depending on which one it was. Actually, this happens most of the time, in most of my conversations, and it does sometimes backfire. I'm not sure if there's a good way to recover if you use the wrong response, as I've laughed when someone asked my name, for example.
Another frequent one is suddenly bursting out laughing when walking down the street or in lectures. It's exacerbated by trying to suppress it, so it usually manifests itself in fairly formal situations, and/or around a lot of strangers. I know that's not exclusively an INTP thing, and I believe it's referred to as "the giggles", but it's probably a product of general social awkwardness. As an example of this effect in action, I had a lecturer who sounded like a Bond villain (complete with Slavic accent), and had a tendency to have his lapel mic too close to his mouth (so it sounded like he was yelling all the time). As he was trying to drive home a particular point, he swung his arms around, speaking frantically about finite state machines, and accidentally held down the "next slide" button on the remote control in his hand. The lecture slides zoomed past, flashing like lightning, and it ended up looking so disproportionately dramatic that I burst out laughing, multiple times, until the end of the lecture. I couldn't go to any more of his lectures, because I would be suppressing laughter the whole time, so I just went by his online lecture slides. For the record, it was a room of 300 people, and nobody else was laughing beyond the first 3 seconds.
The act of putting on facial expressions in front of the mirror for entertainment was mentioned, and that's also something I do a lot of. Consequently, I've developed fairly conspicuous facial expressions, and I've recently become aware that I look extremely grumpy when I'm walking down the street.
Other than that, I guess there's also the matter of missing turns, and walking several blocks too far before realising what's happened. That's not necessarily a bad thing though, as it's varies the route I take at least.
Oh, hey, is anyone else a fast walker? I prefer to overtake anyone walking the same direction. Actually, that's probably to avoid being late (although it isn't always enough to prevent that).
If you read all that, you deserve this elephant:
If you didn't read it, you don't get the elephant.