In Genesis 19, Lot defends the angels who came under his roof against the demands of the local men who want a chance to sodomize the three visitors. From the Torah's description, and Rashi's take on it, it would appear that this was a common practice by Sodomites against new-comers. My question is, wouldn't they have also sodomized Lot when he was a new-comer?
Lot surveyed the whole land and chose Sodom. (Gen 13) He presumably wouldn't have done so if they had such a reputation, let alone stayed if he was actually subject to such treatment.
MORE importantly - Lot arrived in Sodom at a time when he was extremely wealthy (Gen 13). Its very possible that the angels were targeted because they were seen as particularly vulnerable / poor. They arrive in Sodom expecting to sleep in the streets (!, 19:2) and presumably, they looked the part.
I believe this fact - the sleeping in the streets - is a critical element to the story. Its not that Sodomites had a fear of strangers, its that they had a love for taking advantage of the defenseless.
Continuing from @Shalom's point, Lot carried a degree of protekzia by virtue of the fact that he was Avraham's nephew.
So it would seem that he had royal approval, which would in turn, have possibly guaranteed his protection.