origin: In one of Dane Cook's comedy shows, he explains that he was watching two rhino's fucking each other on the discovery channel in slow motion and he could have sworn he saw the male rhino "raise the roof" as if to imply, "Hell yeah...I'm getting some!" To make Dane's imitation of the male rhino more realistic, he uses his microphone as a rhino horn and makes a facial expression, much like a guy would make to his buddy as he's fucking his girl. This whole gesture was taken to another level and is now used to express any kind of excitement, approval, or state of presence. For convenience, the hand to the forehead is used as a prop for the microphone or the actual rhino horn.
Freddie: Are you serious, dude?
Nick: :::does rhino yeah:::
Nick: Where's Chris...he was supposed to be here with the beer 20 minutes ago.
Freddie: Here he comes, Bro.
Chris: :::holds up an 18 pack while doing the rhino yeah:::
Chris: I got laid last night.
Freddie and Nick: :::does rhino yeah:::
Nick: Chris, open the garage door; someone's knocking...
Chris: :::opens garage door:::
Freddie: :::does rhino yeah:::
Chris and Nick: :::does rhino yeah right back:::