Hobo slang for "I'd rather be train hopping," frequently used by hobos all throughout America. Originated sometime in the mid-20th century during the Great Depression. Goes hand in hand with many hobo symbols.
Hobo Joe Junkpan is wandering around a town. He sees Hobo Seasick Steve and hollers, "Bimt!" Seasick Steve knows that this means that he wishes he were cruising across the country, drawing hobo symbols and singing songs. Or attending the Hobo Convention.