Spies at “21” Monday night couldn’t help but snicker at Monica Lewinsky’s choice of seat at dinner — right under a replica of Air Force One donated by former President Bill Clinton. Lewinsky — who as Page Six exclusively revealed is penning a tell-all book about her life and the sex scandal involving Clinton — was spotted dining with friends at the tony Midtown eatery, obliviously sitting underneath the toy presidential jet. The restaurant’s barroom is famously packed with paraphernalia and toys gifted from friends including CEOs, pols and athletes. Onlookers said it wasn’t clear if Lewinsky noticed, but one called the situation “funny.” Her rep didn’t get back to us.