It means to hang out and chill and do some sort of activity that does not require too mucheffort. Usually used in reference to doing drugs or taking mind/body altering substances, but does not have to be used in that content necessarily.
Mike: Hey John, come tone with us for a bit. We are just watching some South Park.
Bryan: Hey man wanna come tone down a bit with me and Paul? (In reference to marijuana)
Joe: Nah man I can't be tonin when I got an 8 am test tomorrow.
Tone really that sensation that r e s o n a t e s through our ears and strikes our soul in such a way that it creates a numbing sensation to the central nervous system
short for Tony Mowbray the single most brilliant reincarnation of all things great of a middlesbrough manager. The envy of the inbred sparn of sunderland, newcastle and leeds fans.
a boro lad: we will win the league with TONE in charge.
a boro geeza: TONE is the reincarnation of al things great for the job without a doubt.