you should give the manager one lame smile... then tell him, "i know u r very loyal but if one day i see you in other company, you must been sack"

or

"Dont worry about me, I will come back to look for you for lunch often but please dont drive your old junk, it is insulting. I will come to pick you up with my Benz, ok?"

or

"Actually I regret leaving this company because I afraid I need to sell my old car for BMW"

but anyway i would recommend to leave some back route for urself... who knows... u might end up under him again in other company or u might go back to this company....