James Cameron slipped into the Imax theater at L.A.’s Bridge theater on Friday tonight as 20th Century Fox showed 16 minutes of his 3-D pic “Avatar” to everyday moviegoers.Fox held the screenings in a total of 101 Imax theaters domestically and another 238 theaters overseas, of which roughly 30 were Imax venues. Tickets were free and were given out during an online lottery. The unusual promotional event-billed “Avatar Day”-is designed to ready fans for the film, which doesn’t open until December, as well as prompt theater owners to install more 3-D screens. Also on Friday, 20th Century Fox announced that the online teaser became the most viewed trailer ever on Apple.com. The first look drew over 4 million streams, breaking the previous record of 1.7 million.