Criticism can be valuable occasionally, so it's good to derive any potentially useful information from it. If there’s nothing of worth in it, just let it pass. Remember that the more criticism you get, the more you’ll get used to it, which will help you to desensitise and deal with it in the future.
“There is only one way to avoid criticism: say nothing, do nothing, be nothing.” - Aristotle
I've heard it said that when someone is very critical, they are also critical of themselves. I wonder if they can turn their criticism on and off? Let's hope so - it's not nice to think that someone would also be extremely harsh on themselves, with no one around to challenge them over it.
'There is criticism that you deserve and criticism that you don’t', according to world famous coach John Wooden. Equally, 'there is praise that you deserve and praise you don’t'. We must judge them both in equal measure.