Mark Zuckerberg had the best view of anyone at Donald Trump's inauguration ... because he was sitting next to Lauren Sanchez -- and staring down at her chest!!!
The Meta owner got caught on camera eyeballing Sanchez's assets while attending Monday's swearing-in of DT as the 47th President in the Capitol Rotunda, along with the world's biggest power-brokers.
Zuck was also seated near Sanchez's fiancé, Amazon owner Jeff Bezos, and Trump's son-in-law Jared Kushner.