When you're texting your friend replying with a lol, and then continue on with your own comment and/or joke, and add another lol at the end for emphasis.
Bobby: Yo did you watch last night's episode of American Crime Story? Shit was bananas.
Suraya: Lol yeah it was good, but I still hate David Schwimmer lol.
Bobby: Them bookend lols can't stop won't stop.
When a "lol" appears towards the start and another at the end of a text to portray a lighthearted tone, yet in reality the sender is likely nervous or passive aggressive.
Examples of Bookend LOLs
"lol I can't wait to see you! lol"
"lol we should go out and grab coffee, then maybe swing by my place later lol"