The girl that your homey is either dating, banging, wifing or has done such activities for a prolonged period of time in the past with any kind of emotional attachment.
It is strictly forbidden -- although such forbidding is mainly unspoken -- to carry on the aforementioned activities on the dead whale.
Doing such things to a dead whale makes you an asshole.
Friend 1: Johnny, why are you macking April? She's totally a dead whale.
Friend 2: Yea dude... your brother still loves her.
Johnny: I'm such an asshole.
Dead Whaling started in San Antonio, Texas, and has been compared to a spastic version of Planking or The Worm. To successfully do the Dead Whale, one must lay down on their stomach with their hands by their sides and begin a series of spastic seizure-like motions using the chest to gain lift.
Concerned Citizen: "OMG! Is that boy having a seizure!?"
Person Filming: "No you moron, he's doing the Dead Whale!"