pee in the wind?
thanks a lot for your kind help~

this scene is really difficult for me， too many expressions that i don't know:(

[Chan: what do I do? I wanna get past this, I don't wanna be afraid of the commitment thing. I wanna go through the tunnel, to the other side!
Joey: Well, ①I've never been through the tunnel myself, 'cause as I understand it, you're not allowed to go through with more than one girl in the car, right. But, it seems to me it's pretty much like anything else, you know, face your fear. It have a fear of heights, you go to the top of the building! If you're afraid of bugs.....get a bug. Right. In this case, you have a fear of commitment, so I say you go in there and be the most committed guy there ever was.
Rach: that makes sense.
Joey: Oh, yeah. Go for it man, jump off the high dive, ②stare down the barrel of the gun, pee into the wind!
Chan: Yeah, Joe, ③I assure you if I'm staring down the barrel of a gun, I'm pretty much peeing every which way.]

3 questions are below...

Question

pee in the wind?
thanks a lot for your kind help~

this scene is really difficult for me， too many expressions that i don't know:(

[Chan: what do I do? I wanna get past this, I don't wanna be afraid of the commitment thing. I wanna go through the tunnel, to the other side! 
Joey: Well, ①I've never been through the tunnel myself, 'cause as I understand it, you're not allowed to go through with more than one girl in the car, right. But, it seems to me it's pretty much like anything else, you know, face your fear. It have a fear of heights, you go to the top of the building! If you're afraid of bugs.....get a bug. Right. In this case, you have a fear of commitment, so I say you go in there and be the most committed guy there ever was.
Rach: that makes sense.
Joey: Oh, yeah. Go for it man, jump off the high dive, ②stare down the barrel of the gun, pee into the wind!
Chan: Yeah, Joe, ③I assure you if I'm staring down the barrel of a gun, I'm pretty much peeing every which way.]

3 questions are below...

Answer

1. From what you wrote, it sounds like the tunnel is a metaphor for commitment in a relationship. So, Joey was saying that you cannot be in a committed relationship when you are dating two women at the same time, which appears to be what he does or prefers.
2. Both of these refer to being fearless. You can use "stare down the barrel of the gun" to refer to being brave in the face of a scary situation. That is a common and accepted expression. "Pee into the wind" is not a common expression in English. If you use it in everyday life, you may get some strange looks.
3. Chandler meant that if he is in an intimidating situation (like someone is pointing a gun at him) he is extremely scared, not brave. This is a reference to how some animals (and people, I suppose) pee when they are scared.

I hope this helps. They were great questions!

Answer

Q: 1. why did Joey say he never went through a tunnel because he’s not allowed to go through with more than one girl? is a tunnel metaphor for something?
2. what do “stare down the barrel of the gun” and “pee into the wind” mean? can we use it in our daily language?
3. what does chandler mean?