When can we start calling ourselves an "ist"?

I was talking to my friend, and I made the mistake of saying "I think I am more of a chemical biologist than a biochemist in the traditional sense."

He said "You're a fricking undergrad. You're neither. What do you mean by that, that you took a few organic chemistry classes and liked them? That's absurd."

Then I said, "You're absolutely right. Right now I am just a student. But what I mean is how I think about science."

He said, "What do you mean, how you think about science, that is ridiculous. I just don't understand what you're talking about when you say shit like that."

But what I mean, I guess, is that in the biology-chemistry interface-land, what is biology and what is chemistry and what is biochemistry and what is chemical biology is totally artificial. But they are words that we use to describe an approach to solving problems, the way experiments are designed, and a school of thought of training.

I mean, one could say "I just don't think like a cell biologist, I think like a geneticist." This means something to me, even though there is a large degree of overlap between what a cell biologist is and what a geneticist is, and a cell biologist better know genetics and a geneticist better know some cell biology. The way papers in Cell are laid out are just different from the papers in Nature Genetics. And not just visually, in the intellectual approach.

Biochemistry is neither biology nor chemistry (although it's both) in a lot of ways. It's kind of its own thing. It's got it's own kinetics. It's got it's own brand of tedious separation chemistry. It's got it's own sort of sensibility. The mindset that I am in when I read a paper from Organic Letters is totally different from the mindset I am in when I read a paper from ACS Biochemistry.

I feel like by junior year, as a student you have a pretty good sense of what sub-specialty of your science training you are good at and interested in pursuing further and what area you are most "minded" like. And as far as I can tell, I'm most "minded" in this relatively new biology-chemistry hybrid business people refer to as chemical biology. Is that so absurd?