I'm getting this sinking feeling you're not telling an entire story here.
Most people are aware Denning is/was a controversial figure in the Gmod community and when his ban from was lifted he acknowledged players may not be necessarily kind to him. That said did you seek out Denning to harass him in game?
Regardless of Denning's past he, like most players, are entitled to be being protected from harassing or targeted behavior by other players.
I think if you are open about the circumstances of your ban would be a great start to it being appealed.
Your Steamid is this btw: STEAM_0:0:634759308