A person that talks absoulte shite and so much of it your brain feels like its starting to melt.

Someone who continuely annoys or irritates someone though speech (usually), this is "melting" them.
The younger melts are described as "mini-melts."
People argue as to the origin of the term "melter" or "melt" but many believe it originated from a man from Belfast Northern Ireland called Christopher who is now known as "Mr.Melt." He was well known for his "melting" powers.
Many people can be considered a "melter" or a "melt."

one who irrates others

when someone irritates friends excessively talking about random things

1. scoring a wonder goal in football
2. putting in a hard days work
3. if someone says or does something ridiculous or awkward

a person who melts, one who lives life in a careless fashion, an optimistic nihilist, a pharmaceutical pill (or any relaxing agent)

a stoner. can also just be applied to someone who's always high on some sort of drug. most importantly a melter has to be noticeably and permanently changed by the drugs they use.