The original pug from Men in Black (1997) was used to play Frank again, but since the pug was now seven years older, they used makeup to hide the gray fur around its nose.
J tells T to "Get married. Have a bunch of kids" and then hooks him up with a waitress (played by Alexandra O'Hara). She is credited as "diner waitress". In Men in Black 3 (2012), the waitress reappears as a housewife with several kids (she is played by the same actress).
J's line on the "driver airbag" ("Actually it came with a black dude, but he kept getting pulled over.") was improvised by Will Smith. The producers liked it so much it even made the theatrical trailer. Barry Sonnenfeld however was not happy, it was played over and over in the month of June prior to the film's release, making the joke old and tired by the time people saw it in the movie.
In both Men in Black (1997) and Men in Black II (2002), a tandem bicycle decorated with lights can be seen going past the pawn shop. The bicyclists are actual residents of this area of New York City.
The diner that Will Smith takes Agent T and Laura to has the spaceship from the giant cockroach from the original film is sticking out of the roof.
Michael Jackson: as himself as Agent M, an undercover Man in Black. Jackson was a huge fan of extra-terrestrials, and there was speculation about him being an alien.
Chloe Sonnenfeld: Barry Sonnenfeld's daughter appears as Elizabeth, the young Rugrats-loving girl at the post office. She also appeared as the hippie girl who meets 1969 Boris at Coney Island in Men in Black³ (2012).
Biz Markie: The postal employee/undercover alien, who has a beat box conversation with Agent J. He and Will Smith were rappers in the '80s.
Osseus Labyrint: In one scene in MiB headquarters, two aliens in black bodysuits can be seen walking around on all fours with their limbs straight, bobbing their heads up and down. The two aliens are played by an interpretive dance duo, who toured with the band Tool, and appeared in the band's video for "Schism" performing the same move.
Rick Baker: at MiB Headquarters at the Alien Registration counter, he can be identified by his trademark ponytail hair.