A couple ideas. First, you could have the guardians of the time-stream come after him, be they paradox eaters, langoliers, Marvel's Time Variance Authority (or TVA), etc.
Alternatively, and possibly more fun, change his world. Little changes that won't ruin it for everyone ... at first.
"That great hot dog place isn't there anymore."
"I could have sworn the neighbor's dog was a basset hound, not a dachshund."
"Hey, my hunter got deleted!"
Then ramp it up as he gets reckless.
"Final exam? I'm not even in this class!"
"Dude... where's my car?"
"Hey, all my toons are horde!"
And finally, the big stuff.
"Mom, Dad, don't you remember me??"
"President Palin???"
"You've never heard of World of Warcraft? How is that possible?"