Shy guy or not interested how to tell for sure?

Calling all guys!!! Is there any sure fire way to test a guy to see if he acts a certain way around a girl b/c he is shy or not interested? How can you tell if avoiding eye contact or avoiding the girl altogther or being nervous and uncomfortable around a girl is b/c he is shy or just not interested?

In my situation he doesn't look at me when speaking to me
-when I wore make up for the first time and he noticed and told me that I looked good. This rised my level of interest in him and it made me feel great
-I try to bump at him at work often and when I see him I say hi and all I get is hi back not much else
-yesterday when I saw him at work while he was finishing his shift and there were also few co workers with me .He didn't even look at me at all and didn't say anything to me :(

He is just not interested?

I know you wanted opinions from the men of the forum but Oh god I hate that awkwardness... Why don't you just strike up a conversation with him anyway, maybe throw him a compliment like 'you're looking smart today' then perhaps when you feel comfortable ask him if he fancies going for a drink (or whatever) after work. Check out his reaction. Its difficult isn't it when you cant quite figure them out. But the fact he noticed your make up may indicate he likes you... Good luck.