Derivatives include 'lol' and 'rofl'.
The most frequent time for this phrase to be used is when hungover with friends, laughing about the previous night's antics. Usually in this situation the participants are too rough to be in any position other than vertical.
Whilst not vital to using the phrase, beds are commonly involved. However, users may also exclaim 'LIBL!' while slouched on other items of furniture.
Popular in Yorkshire but spreading towards the Midlands at considerable speed.
"Girrrl I just saw you LIBL"