I always have the same advice: practice some smart replies.
Dress sense: yes, I have always ploughed my own furrow
Timing: crikey, are you stalking me?
Smiling: not surprising given the company I am forced to keep
Or just one, nicely PA right back at them: Should I care what you think?
Literally make a list and practice. I worked with a total pillock and took my own advice. It annoyed the hell out of him, but he could never articulate why, which seemed to annoy him more.
I did also speak to my line manager and HR, to explain that a colleague seemed to be overly interested in how I did my job and that I was uncomfortable with the idea that he was making loud judgements about me and my work. He was spoken to, which made him worse, but our line manager basically told him to grow up.
By making daft responses I managed to change how I felt about his comments. I felt sad for him and his snippy little life rather than intimidated by him. But it took persistent practice, which eventually became a natural response to his comments,which did eventually stop.