At the very beginning, when Tommy Lee Jones and his elderly partner stop the vanful of illegal immigrants, they take the blue multi-flippered alien over a ridge to talk to him, er, it. When the nosy Border Patrol agent comes to have a look, the alien freaks out and attacks him. Why’d the alien react that way? It had been very easygoing with the two MiB agents.
I assume it intended to use him as a human shield, and escape these two agents. After watching the whole movie, you might think, “Go ahead big blue, we’ll eventually catch up with you, and neuralize the entire city block if we have to”, but at the beginning of the movie, we all wonder what’s going on, and K has to splatter the alien. Basically, MIB agents are super-cops/judge/jury/exceutioners, for aliens that choose to live on Earth. And can do anything. And the aliens know that, and insist on acting out sometimes, in hopeless defiance.
Gee. If you really study the movie, it’s pretty sad. Glad I only watch it for the puns, snappy comebacks and meta references.
It’s kind of like a happy, comedic Blade Runner.
If you’re gonna get all paranoid and deconstructionist and junk, you should add that there’s no reason to think the MiB have any sort of legitimate authority. They’re not even a rogue agency at this point, as they operate without legislative, presidential, or judicial oversight. They’re a law onto themselves, and one day Z will just say, “Screw it. I’m making myself god-king of Earth.”
I always just figured it didn’t want witnesses. The MiB were fine since they were Clued In, and they have Big Guns, but normal humans couldn’t be allowed to know about the alien’s presence. That reasoning always seemed shaky to me, though, since a more rational creature would have let the MiB deal with its own kind.
“Oh, Mr. Veedal! We are The Telephone Company! We are not subject to any local, state, or federal regulation. We are omnipotent!”
Also, the “alien” was evidently know to K and D and they to him. “Mikey” was just trying to get away from what was coming.
When the INS agent intruded, Mikey no doubt thought that this was gonna keep him from leaving the planet. So, he reacted.