I'm not sure if this question is on topic (maybe it just needs to be rephrased), but since this made global headlines due to the Dalai Lama not being able to understand it, I figure most non-native speakers would have trouble getting the joke too.
This is the joke on YouTube. [1]
The Dalai Lama walks into a pizza shop and says "can you make me one with everything?"
As can be seen, the Dalai Lama was a bit confused. The thing is, I don't get it either. Is there some sort of pun in there somewhere? Can someone please explain to me why this is a joke?
The joke here is the use of the phrase one with everything.
It can be used with either of the following meanings.
spiritual: to be one with everything means to be unified with everything else. This is a main concept in Buddhism, Hinduism, etc. where one feels that everything else is a part of self. To be one with everything is one of the higher aims of such religions.
The other meaning of the phrase is to get a pizza with every (available) topping.
Now, I posted this answer after a perfectly good one was already given, because I wanted to stress (as a native from a mostly Buddhist country) that "to become one with everything" is not really what a Buddhist aim for. It might be what Anglo-Saxons stereotypically see Buddhists aim to do, though.
You see, the souls of gods, spirits, humans, mammals, insects, plants, even old rocks and mountains reincarnate with one another. In that sense, we are already basically the same with everything else. The aim of a Buddhist is to overcome this infinite chain and get out of it, by attaining enlightenment.
So it is not really about making one with everything; it's more about making oneself nothing.
(It's not that I'm preaching that it's the correct way toward the world; I don't really believe in it myself. I'm just saying it's what Buddhism is about and I just want readers here to understand it.)
The joke here is that this phrase has two meanings, depending on the context.
Becoming "one with the Universe" is a sort of a stereotypical Buddhist concept. The Dalai-Lama is the accepted head of the Buddhist religious hierarchy in Tibet (if you aren't Chinese). So becoming "one with the universe" is something one can safely assume he is interested in.
When ordering a food item (e.g. burger, pizza, burrito), if you want every topping the establishment uses you would typically tell the server "I'd like one (whatever) with everything."
Now, Universe and everything are more or less synonyms. So, if the Dalai-Lama were to say such a thing in the proper context, it could have either meaning, or perhaps both.
Edit: Check out this youtube clip [1] at about 1:20. An English interviewer tries to tell this joke to the Dalai-Lama himself. It went over about as well as Yuji predicted it would.
[1] http://www.youtube.com/watch?v=3KNpn-XGM04&feature=endscreenThis is the joke:
Hmm .. a similar joke, which I think predates the above joke:
What did the zen master say to the hot dog vendor? Gimme one with the lot!
I really like that joke, it's clever. The idea is you expect the answer to be something clever, a pun, etc. But a zen master just has no interest in idiocy like being part of a "clever" joke, or the like. He just wants to totally and completely partake in life, so he just immediately orders a great big fat hot dog.
This new joke ("make me one with everything...") is an ingenious play on the pop-zen notion one with everything, one with the universe - but I think it's shallower (it's merely wordplay) than the possibly earlier joke (which aims to whack you in to satori! :)
Some people are asking why he didn't talk about buying a hot dog with everything.
I don't want to overstate my answer, because certainly we do have hot dogs and hot dog shops, but it's not exactly an every day food, it's not really our culture to eat hot dogs, whereas we do eat pizzas all the time and you would say it is part of our culture.
It would be pretty weird if he chose to make a joke about hot dogs, not that trying a pun with anyone ESL, especially the most holiest man in the world, isn't already pretty weird.
We tend to say a pizza with the lot, but a pizza with everything is not much of a stretch.