Jon Gosselin -- Here's Why I Bought 'Call of Duty' Game at Kate's Yard Sale

Jon Gosselin has spared himself the humiliation of buying his video games back from his ex-wife at her garage sale ... by playing a serious mind game on himself.

We got Jon arriving at LAX Monday and he was quick to say ... the money he shelled out at Kate Gosselin's yard sale to retrieve his "Call of Duty" game was NOT payment ... it was a charitable donation.

Kate was raising money for an animal rescue group. So Jon helped the dogs, and got doody in return.