The only instance where I can think of where he quote-unquote "buried" someone in the ring was at the Great American Bash in 07 or 08 when he just went in and tore apart Miz for most of the match. Keep in mind he was the top guy in the company and had a 1-2 month feud with The Miz when the guy was still wearing customized jorts to the ring and went "HOO-RAH!" I think Cena was still injured or was filming a movie when the feud started,and he went along with it even though most main eventers would have returned expecting to be in the main event. Hell,it wasn't even a clean squash,Miz was able to perform most of his moves.
Other than that,I can't think of any instance of a squash match involving Cena. He's more often than not,allowed his opponents to perform their moves and he's always sold them like he would in a big match. His match with Dolph Ziggler last year or in 2010 was pretty good for a Raw match,and I don't think he's ever buried anyone popular backstage either. He was one of the first guys on the Zack Ryder bandwagon and he's still plugging Zack Ryder merchandise and his twitter from time to time,and if reports are to be believed,he was pulling for the summer feud with CM Punk.
And I wouldn't call him ultimately defeating Nexus after 6 months a squash. When he faced them 7-on-1,he always got his ass kicked. He even had to join them for a while,until he finally got the group separated from one another and beat them with the help of others,before finally beating Barrett at TLC. Hardly a squash feud.
It's rather contradictory when people complain about Super Cena and complain about Cena squashing his opponents. Super Cena makes super comebacks from beatdowns delivered by his opponents. A squash means the wrestler gets in the ring and beats his opponent mercilessly for the most part and then gets the pin.It's either Super Cena or Squash Cena,it can't be both. As for not losing cleanly,the sad truth is that top faces don't usually lose clean. Take for example CM Punk. His losses at PPVs and recent matches after Money In The Bank haven't been the cleanest. Lost to Del Rio via cash-in; Lost to Triple H after Awesome Truth interfered,attacking both men,but interfering nonetheless; Lost to Del Rio at Hell In A Cell after ADR used a lead pipe on him; Lost at Vengeance after interference from Kevin Nash; Lost to Ziggler twice after John Laurinaitis interfered in both matches. It's just the way it goes. The controversy helps to lengthen the storyline. Clean finishes at main events seem to be mostly reserved for ending big feuds.