To be on Robitussin and drunk at the same time. To be under the influence of the chemical DXM and to be under the influence of alcohol at the same time. Comes from the beginning letters Ro of Robitussin and the end letters nk from drunk, put together.
Guy1: "dude i was so ronk last night!"
Guy2: "wtf, who just gets ronk bro?"
Guy1: "dude, i got so ronked last night"