David Beckham -- I'm 52 Times Cooler Than My Son! (VIDEO)

Brooklyn Beckham is developing quite a following on social media, but he's nowhere close to his father David ... which pops was sure to remind him of ... in the most embarrassing way possible.

The video's hysterical ... 16-year-old Brooklyn posted an Instagram video to celebrate crossing the one million line. David just had to poke his head in and put his son in his place ... by reminding him that 52 million people follow him on Facebook. BTW, David inflated it by 2 mil.

Brooklyn's reaction is classic.