Is an alternative word for
plastic/fake.
Referred to people who are "plastic" (
barbie). They only care about themselves, they think that everyone should have a perfect body shape, everyone has to be perfect.
Flastins are very superficial, annoying and never say the
truth.
Flastin is the perfect name for those people who aren't real, they are so plastic that even the plastic is more real.
That's what makes them flastin.
To sum it up, flastin is "fake plastic people".