It's common slang for a huge 18-wheeler
It doesn't take a BIG man to swear, it's takes a BIG man to 
convey his thoughts ... Big Rig -Could mean "18 Wheeler" or "Fancy, expensive 
radio" ... Because sideband is so sensitive, it is a common practice to "open" the... [DOC] [TLE] Trucker Talk | Highway Hags [PAR] Or get yourself a big old CB and drive down the highway flowin' and goin' with 
your new best friends the .... Squirt gun: Have heard this term used for a firetruck, 
but its not as common as some of the other terms.