We are learning from Case Studies in Business Ethics by the late Rabbi Dr. Aaron Levine z"l professor of economics at Yeshiva University.
"Moral training against selfishness begins with the notion that denying one's fellow a benefit when it costs one nothing constitutes obnoxious conduct. The sages identified such conduct with the sin of Sodom."
Case: A meets his neighbor B at an affair many miles from their respective homes. A drove with his own car while B hired a car service. Neither knew that the other would be attending. A offers B a ride home.
A had originally planned to drive both ways by himself and incur all costs of gas and tolls. It is ethical for A to now ask B to share the expenses with him?
Rabbi Levine writes that demanding B to pay for his ride in this case would be an example of the attitude of Sodom.
If the common practice is for B to offer to pay then dropping a hint to B that he should pay would not be "obnoxious" but merely unsociable and ungracious conduct.
However, it is the "gentlemanly" or even expected for B to offer to pay. But he is certainly not legally required to. He is not even ethically required to. For him to offer to pay would conducting himself above the letter of the law.