A slang term used to denote people who spend excessive amounts of time socializing, loitering and wasting time in subterranean tunnels which are primarily used as a means of transportation.
Originated from Carleton University - Ottawa, Ontario, Canada. The Carleton University campus is linked by subterranean tunnels which provide faculty, staff and students with a means of transportation. All buildings are connected to these tunnels thus providing a clean and warm environment which is often favored over walking through rain or snow.
Tunnel rats are most often students who live in residence and rarely change out of their comfortable pajamas. Since food, banking and even a barber shop are all within reach, the tunnel rat may live indefinitely without having to step outside. The more common form of tunnel rats are those that hold small social gatherings at locations which create a bottleneck during rush hour. Combined with the golf carts which regularly travel through the tunnels, these vermin grind traffic to a standstill and infuriate local students who require a prompt means of transportation.
"Jessie's a tunnel rat. She never hangs out at the campus pub and I'd be surprised if I saw her wearing anything but those filthy plaid pajamas."
"I was late for my lab again! I encountered a pack of tunnel rats and I left my cattle prod at home."