The opposite of hilarious, but in a special way. When a friend is laughing at you, or you are the brunt of a joke, THEY think it's HI-LARIOUS but you, as the brunt of said joke, think the opposite - therefore to YOU, it's LowLarious.
A relationship that is on the low, or under wraps. Usually nobody knows, and this information is only shared between the two individuals on each end of this relationship.