"You were already having been going to do that!"

From one of the Futurama episodes:

Farnsworth A: You people and your slight differences disgust me. I'm going home. Where's that blue box with our universe in it?

Farnsworth 1: Oh, you'd like to get back to your evil universe, wouldn't you? And destroy your box with our universe inside it.

Farnsworth A: Nonsense! I would never do such a thing unless you were already having been going to do that!

The part in bold: is it grammatical, or is it just an intentional word play by the scriptwriters to emphasize time travel?

It is indeed an "adjustment" of English grammar having to do with the complications of time travel. When causality in the future has its effects in the past, conditional statements become complicated. Perhaps the best comedic exploration of the effects of time travel on language was by Douglas Adams in The Restaurant at the End of the Universe:

One of the major problems encountered in time travel is not that of accidentally becoming your own father or mother. There is no problem involved in becoming your own father or mother that a broad-mided and well-adjusted family can't cope with. There is also no problem about changing the course of history—the course of history does not change because it all fits together like a jigsaw. All the the important changes have happened before the things they were supposed to change and it all sorts itself out in the end.

The major problem is quite simply one of grammar, and the main work to consult in this matter is Dr. Dan Streetmentioner's Time Traveller's Handbook of 1001 Tense Formations. It will tell you, for instance, how to describe something that was about to happen to you in the past before you avoided it by time-jumping forward two days in order to avoid it. The event will be described differently according to whether you are talking about it from the standpoint of your own natural time, from a time in the further future, or a time in the further past and is further complicated by the possibility of conducting conversations whilst you are actually travelling from one time to another with the intention of becoming you own father or mother.

Most readers get as far as the Future Semi-Conditionally Modified Subinverted Plagal Past Subjunctive Intentional before giving up.