Sorry for the thread necro. I wish I had this resource when I was running my own campaign world on a regular basis as this question actually came up. As someone who is an actual nudist I recognize some stereotypes here.

AC effect - this needs to be considered on a case-by-case basis. In a battle the effect of simple cloth does not contribute well to any defense unless layered. In fact some forms will tend to hamper defense if they are too loose or flowing (inertial effects and obstruction as well as a chance on the clothing getting hung or caught on an item). Humans have actually been fighting very well in the nude for millennia actually without ill effect. Additionally there is reduced encumbrance for the person. I'd argue no effect on AC other than a slight dexterity bonus and reduction of exhaustion penalties. Of course certain hazards pose penalties for a lack of protections (like footwear). Thorns I've dealt with in real life and I've had shirts and pants caught on the thorns in a manner that has made the hazard worse. Gloves and tools to combat the thorns work better. Again, the DM needs to consider the totality of circumstances here.

Constitution - Actual research and experience has shown that the body's ability to regulate temperature improves with lesser amounts of clothing. With regards to rain the body dries faster (clothing tends to hold onto moisture for quite some time). Over time the skin gets better in adapting to environmental effects like sun, etc. - it evolved to do that. There should be an initial penalty for someone who has just started "dressing" in this manner but it should vanish fairly quickly. There may a bonus afterwards but it would be slight. There is an interesting bonus with regards to contact poisons, hot oils, and the like in that there is a likely saving throw bonus. Why? Because there is nothing to cause sustained contact after the initial exposure. One of the things that is part of emergency procedures is removing any articles of clothing in the area of exposure. While there is a joke about cooking bacon or other oily foods, it can be safer to do so in the nude. The only really safe way for that is to wear a full body suit that is insulated and impermeable with a decent face shield. :) Otherwise any exposed skin (and the eyes) are subject to grease splatter.

Social interactions - This depends entirely on the culture. Nudity used to be quite common in the Western world among the average farm worker and the like. Clothing was expensive and difficult to get so it was treated accordingly. The average RPG is often in ancient settings so the effect of nudity may be minimal or non-existent. In some instances it might be an aid. Consider the issue of tattoos instead of clothing, for example. The covering of such might cause issues if they are socially important. Same goes for body paints.

Refusal of Service - This is just an extension of social interactions. Much of the U.S.'s "No shirt. No shoes. No service" was a result of events and practices during the 1960s. Until fairly recently you could go out to eat naked in San Francisco (I think some of this license still exists there but my memory for details is hazy).

I don't think I've a great deal to the original discussion other than giving some additional circumstances to consider. YMMV.

I wish I had this resource when I was running my own campaign world on a regular basis as this question actually came up. As someone who is an actual nudist I recognize some stereotypes here.

Here is my answer addressing the points in the original question:

AC effect - this needs to be considered on a case-by-case basis. In a battle the effect of simple cloth does not contribute well to any defense unless layered. In fact some forms will tend to hamper defense if they are too loose or flowing (inertial effects and obstruction as well as a chance on the clothing getting hung or caught on an item). Humans have actually been fighting very well in the nude for millennia actually without ill effect. Additionally there is reduced encumbrance for the person. I'd argue no effect on AC other than a slight dexterity bonus and reduction of exhaustion penalties. Of course certain hazards pose penalties for a lack of protections (like footwear). Thorns I've dealt with in real life and I've had shirts and pants caught on the thorns in a manner that has made the hazard worse. Gloves and tools to combat the thorns work better. Again, the DM needs to consider the totality of circumstances here.

Constitution - Actual research and experience has shown that the body's ability to regulate temperature improves with lesser amounts of clothing. With regards to rain the body dries faster (clothing tends to hold onto moisture for quite some time). Over time the skin gets better in adapting to environmental effects like sun, etc. - it evolved to do that. There should be an initial penalty for someone who has just started "dressing" in this manner but it should vanish fairly quickly. There may a bonus afterwards but it would be slight. There is an interesting bonus with regards to contact poisons, hot oils, and the like in that there is a likely saving throw bonus. Why? Because there is nothing to cause sustained contact after the initial exposure. One of the things that is part of emergency procedures is removing any articles of clothing in the area of exposure. While there is a joke about cooking bacon or other oily foods, it can be safer to do so in the nude. The only really safe way for that is to wear a full body suit that is insulated and impermeable with a decent face shield. :) Otherwise any exposed skin (and the eyes) are subject to grease splatter.

Social interactions - This depends entirely on the culture. Nudity used to be quite common in the Western world among the average farm worker and the like. Clothing was expensive and difficult to get so it was treated accordingly. The average RPG is often in ancient settings so the effect of nudity may be minimal or non-existent. In some instances it might be an aid. Consider the issue of tattoos instead of clothing, for example. The covering of such might cause issues if they are socially important. Same goes for body paints.

Refusal of Service - This is just an extension of social interactions. Much of the U.S.'s "No shirt. No shoes. No service" was a result of events and practices during the 1960s. Until fairly recently you could go out to eat naked in San Francisco (I think some of this license still exists there but my memory for details is hazy).

Please note I refer to "slight bonuses" where I assume DM discretion. This can be as little as +0 to as much as +2 typically. This term has been used in official magazines and other publications since the earliest days of D&D.