Purposely sniffing sharpie markers is very bad for your health and can actually get you high and could cause brain damage.
You should never purposely sniff sharpies because it could lead to brain damage, dizziness, slurred speech and lack of coordination.
Smelling the sharpie just once should do no harm but do not make a habit of smelling or sniffing sharpies because that's never a good thing.
The Sharpies contain volatile solvents, which are liquids that become gases at room temperatures and can cause serious health issues.
Just like sniffing paint and other things that are bad the chemicals in Sharpies are bad to sniff or breathe in and should never be done.