"Robo is slang for Robitussin, which some people drink to get high." - Craig Finn. It's also a short form of the name "Robbie Robertson."
The lines "blew red...into a tissue" and "over the counter" also likely reference the recreational use of Robitussin.
May also refer to the drummer from Black Flag and The Misfits, ROBO.
from The Swish