If a guy gets nervous when you approach him, it is very natural.
Because when you speak to someone, you always enter in their personal space.
This happens naturally.
Without realizing it or truly wanting it, you use your "conquering power" when you start chatting with someone.
If you want a man to feel comfortable, give him space.
Give him time to adapt to your presence.
Humor and teasing is a good way to get everyone relaxed.
Chat a bit, let go.
Play with that.
There is nothing to worry about.
People tend to build walls around them.
It is a sphere of protection.
When you break through this protection, they naturally feel defenseless.
A new balance of power and energy gets built up.
It can take a couple of minutes for this energy to find a new balance.
There is another element as well: they can be excited by your presence.
His lack of confidence can show as if he was not comfortable.
Can you see that?
It is true, the one who takes the initiative (Especially if you show lots of assertiveness) uses this conquering power.
You basically go beyond his comfort zone and connect.
The one who is waiting and receptive is within a sphere of comfort and by coming into their sphere, you challenge this comfort.
Again, there is nothing wrong with that.
Give it a couple of minutes to readapt.
Play with humor.
Teasing and if you feel you make guys uncomfortable, show less assertiveness in your approach.