gas that diesel down

Common meanings:

To "drink an energy drink".
To get excited about something. To get prepared.
To be ready.

"I gassed that diesel down before this football game."
"I'm tired enough to gas that diesel down."
"Look at Tommy gassing that diesel down"

big whiffer

Someone who enjoys smelling other people's aromas.

"Yeah, my man's tony? He's a big whiffer, always trying to smell other people's stuff."