Restore Lion on MacBook with Sierra on it
While ignoring this is not such a good idea security-wise, you can only downgrade a macOS with an external medium (Disc, USB-Stick) while erasing your hard drive completely.  


Since you no longer own a copy of Lion,
you need to buy it in the Apple Store: Link
You also need a USB Stick with 8GB of Space  





Purchase the Copy of Lion from the Apple Store
Redeem your code in the Mac App Store
Download your copy of Lion, you will see a "Install Mac OS X Lion" in your Applications folder.
Download DiskMakerX aka LionDiskMaker
Point it to your Copy of Lion and your 8GB Stick
After finishing restart your mac and press alt as soon as the screen flashes
Start the USB Stick (Lion Installer)
Open Disk Utility in Menu --> Utilities and erase your hard drive
Install OS X Lion
Be happy with your old OS