If your foot brushed against mine I would not show any indication that I noticed and then way way later like for your 40th birthday I would send you a letter that said
"Dear Pats,
I wish you a happy birthday and also wish that you were able to maintain stable walking strides with both control and elegance. On December 28th at 8:23pm 2016 your foot brushed against my heel and I wanted you to know that I found it rude.
Regards,
DK