I don't think of laughter in terms of something that turns me on or off in the first place but I think those people are usually immature and probably a bit mentally defective so you could say it's a turn-off..
I have mixed thoughts on this one. In one respect it can get a little annoying. But in another respect it's good because it shows me that the person isn't afraid to show vulnerability and vulnerability is a very important trait. If they do it more out of anxiety then this is also good because it basically means that I'm in control of the interaction more. If I'm in control, I tend not to use that advantage to exploit or manipulate so I trust myself with power. But other people, I do not trust with power, therefore it is usually better if I am dominant. So frequent laughter, on the whole is a positive trait.
I'm guilty of this. I don't do it on purpose I just can't help but laugh at almost everything. I've noticed that this happens mostly when I'm with my friends I guess it's because I'm really comfortable with them and I get overly expressive? Although, I never force myself to laugh.
Yep I see guys do it all the time, face red and all when flirting lol... just awkward man. But I laugh when i find something funny. Even in public... something rude or obviously not even funny to others haha. For example, some idiot riding a bike in socks and sandals... not funny to the majority but we'd just piss ourselves xD