I hadn't been watching him too closely this season and was willing to give him the benefit of the doubt on that stunt play. But from that same user's vine, here are two plays from the Miami game where he looks slow off the ball and generally unenthused.
https://vine.co/v/ePu3pMAA1HU
EDIT:
Actually, this vine user has a lot of videos of McMullen looking mediocre:
https://vine.co/v/eFjpOdD2IIt
https://vine.co/v/eFDPJjJHn50
Yeah, those don't look great for sure. But also, it'd be pretty easy to pick out four of five plays of every single player that make them look silly. And as illustrated earlier, you have to look at all their film and weigh it all out. I don't study the DEs during the game, but I'm sure McMullen has had a few real nice plays too. He was credited with a forced fumble against Southern Miss. On the other hand, some people I respect are also questioning his play so who knows.
I'm not saying a change shouldn't be made if we have a better alternative. But I hate throwing players under the bus without knowing what's going on with them. McMullen deserves fans support for the effort he does put in, even if it's not starter-caliber. He doesn't deserve social media ridicule from guys who break a sweat getting off the couch to grab the chip bowl.
This mini-rant isn't directed at you wanderful, just throwing it out there.