20. "And I Run"
Easily the best hidden joke of the entire film comes in the Egyptian sequence following Apocalypse's escape and his attempt to recruit Storm. When she is chased through the marketplace for stealing, an Egyptian 80s pop song plays from a radio.
Hilariously, it's an Egyptian version of A Flock Of Seagulls' "I Ran", matching not only the chase scene, but more importantly the fact that Nightcrawler's hair is inspired by their lead singer.
Incidentally, Storm's mohawk hairstyle was first introduced in 1983 by artist Paul Smith - the same year Apocalypse is set.