I will start-
1) How main girls are okay with being nude/semi nude openly before others or tolerating sexual harassment from other characters. For example,
-Rias and Asia are okay with being semi nude wearing naked aprons before Issei's father although just before this Rias outs Issei's mom from changing room when changing into that apron from her dress.
-Akeno wearing a skimpy dress and performing BDSM play with her father Barakiel and Barakiel getting turned on by it while screaming his wife's name in ecstasy. The same Barakiel who scolds Akeno for wearing that skimpy BDSM outfit and playing with other members just before this scene.
-Issei getting angry at Odin for ogling at Rias' chest and Akeno's panties, but being okay with Akeno wearing skimpy outfit and doing BDSM play with other sacred gear members and her father, when he is tied and made it watch in some other room. This is like some kind of NTR torture play designed for Issei by Grigori in the future in which Akeno will have a BDSM play with her father and sacred gear users and NTRs Issei who is tied down with a rope and watches that mental torture. LOL
-Issei always making rias go nude in front of other guys while simultaneously saying that he doesn't want others to watch her chest, etc.
-School girls being okay with perverted trio's schticks and not reporting them to school authorities and police.
2) Unrealistic increase in power for Issei.
3) Issei still being less confident while being super powerful. etcetra.
What are some other unrealistic things that annoy you when they are not consistent with the series?