Really when searching for the answer to this I found several problems. I had to look deep inside myself and ask myself the hard questions. Perhaps the moustache grew Splinter on the end in another time when moustaches were born and children grew on them? Was it from the sewers where Splinter spent his childhood chasing rabbi mice to feed the starving mole rats that live in his stomach? Could Jebus microwave a burrito so hot that he himself could not eat it? Or perhaps Splinter has weapons of mass destruction hidden in there to help save his former lover, Saddam Hussein's ass? Was the moustache invented by the Iraqis as a way of exporting rabbi chipmunks to the starving villages of Borneo for them gain their confidence before snatching away their sugar caves from under their noses as they feast on the rabbi chipmunks and then smuggling them to the cane fields of Vietnam by way of the moustache? Perhaps it was invented and implanted on his face by the Board of Studies to make students do exactly what I'm doing, lose focus on their HSC and study the reasons for its existence and then scoring a poor UAI and having to work in the underground sugar caves of Vietnam. This would be part of the cheap labour agreement that Molly Meldrum signed with the evil Warren who took on the form of a 12 year old Viet prostitute who then challenged Molly to a boat race in which the winner received the right to exploit members of the losers country for cheap labour. This would have worked well but the evil Warren lured Molly to his fate with a alluring feast of RatSack kebabs on the eve of the race.
So which of these theories proves most correct you ask?
None
The moustache was actually the hair from the armpits of Fran Drescia (The Nanny), which Splinter stole to sell on Ebay to recoup gambling debts during his time working on the set of The Nanny. He planned to glue them to his lip to smuggle them into Australia but during transit became addicted to the smell of them and as such now must sniff them constantly in order to prevent becoming a hideous Mole Rat on the last Monday of each month. This was the result of a bite he received while collecting rabbi mice in the sewers of Bangkok as a child.