He couldn't say why he liked it. Grimmjow wasn't one for giving away control, so for him to do this with the soul reaper…he was sure it said something about their relationship that he was not ready to realize—may never be ready to realize.
Plus, it wasn't like they did it all the time. They tended to have rough sex, sure, but they only ever did this particular thing when they were both stressed or frustrated.
Hisagi could be blamed for it all, in his opinion. Grimmjow may never have discovered that he liked this—having a hand on his neck, fingers gripping tight enough to bruise, his air supply being slowly cut off—if not for that day on during the war, after he fought Ichigo and ended up meeting Shuuhei.
At the time he had felt the slightest tinge of pleasure, but it wasn't something he focused on at that moment because there had been bigger things to deal with than the possibility that he might like to be choked.
They didn't get together until the second year after the war, and even then it was purely physical. The hand to the throat while in the throes of passion, well, that happened after a bad first contact in the human world, and it had been by accident, really. He hadn't meant for it to go through, just like he's sure Hisagi hadn't meant to actually follow through with the—admittedly—vivid image that he had portrayed. But, their frustrations had been running high…
Placing a hand on his throat as he stared at the ceiling, he wondered how he could get Hisagi to do that again. Things had been going well lately, but he was looking forward to a little rough action. The thought of being out of control…well, he'd never wanted that feeling more.
