The best compliment you can ever get from a mathematician.
For those of you who are confused, here's an explanantion:
All mathematicians, whether
pure or applied mathematicians, will have studied their fair
share of
pure mathematics. Many mathematical theorems (statements that are shown to be unquestionably
true) are of the form "There exists something in some collection of mathematical objects such that amazing property is
true". This type of theorem is called an existence theorem. Essentially, when a mathematician says "WOW! YOU EXIST!" to you, they are refering to these existence theorems and that you're amazing.