LB stands for "Little Boy', commonly paired with LG for 'Little Girl'. The term was adopted and bestowed upon the youths within the Asian-Australian Community most likely due to their smaller frames. Whilst not all LB's and LG's fit this description, you may notice an LB by his 'modded' car, diamond earrings, Gucci and/or Louis Vuitton accessories, and chiselled jaw as a result of attending many Hardstyle and Trance events.

when you've done something so cringe you can't stop replaying it in your head and it stops you from getting on with your every day life

It means like back.
Usually used on instagram

meaning "little bitch". Often used to describe whiny, complaining Noobs who are constantly bitching.

aka Little B*tch; (noun) Person who seeks eternal attention, confirmation, has a sense of entitlement and who quickly blames others for any unpleasant events which happen within their lives. Warning: extended interactions with said person will cost a large portion of your time and/or money with no gain and possibly lower your self esteem as everything will be your fault.

In a Fraternity, "LB" means "Line Brother".

Little Boy; Often used when describing a male being too cocky or Immature for his age. Hanging around older women and trying to look older for his actual age.