I also try to meet other people within the design industry thinking that we can possibly collaborate.
Sometimes I get a warm response, or friendly rejection, but there are those times when some people are downright rude or insulting. The only explanation I have for that is that they are paranoid (if we are looking for similar clients - like I often look to printers for work) or they are not very confident in themselves and what they do.
Confident people tend to be friendlier in my experience. They know they don't need my services, maybe because they have another graphic designer, so they may nicely say "Thank you for inquiring, and good luck in your search."
I never understand people who come across as condescending or offended and practically insult me. The sad thing is THEY could have been MY vendor, or a referral source for my clients. I don't want to do business with someone like that, and certainly not be the one who refers them if they treat everyone that way.
My opinion is that there is enough work to go around, and there are varying personalities - some who may not want to work with me, may love one of my colleagues, and vice versa.
So, I go forward, with a positive attitude and a smile on my face (you can HEAR that on the phone, you know!)...