My most sincere.

Thanks a million.
It’s such an insipid insincere expression, isn’t it?
Thanks a million. Like a virtual verbal air-kiss.
Mwuh! My fake spit is my gratitude.
I never say thanks a million, though I might say thanks a hundred. Or maybe thanks six.
Thanks ax2+by2+c.
Thanks a parabola.
Thanks a huge enormous biggest ever in the whole world hyperbola.
Thanks infinity.
Thanks a hankering.
Thanks a brain freeze.
Thanks an ounce. Thanks a bunch. Thanks a scab.
Thank heaven. Thanks ever so much.
Thank the academy.
Thanks a hail of bullets.
Thanks a reign of terror.
My favourite of all, and the one I use most often is this: Thanks.