Okay, this is about my girlfriend, so I don’t have a ton of room to actually talk about this but here it goes: Are bikinis sinful? She recently bought one and I was wondering if I should be at all concerned with her wearing it. And it’s not just a regular bikini, it has a little more translucent cloth in the lower area. Like I said, I don’t have a ton of room as far as her wearing it, but I wanted the Catholic perspective on this issue.
I’m afraid that, in this case, your personal reason for wanting to know the answer to this question cannot be separated from the principle. I believe that it is possible that you want to know whether bikinis are modest either because you want to know whether or not you should be expressing disapproval to your girlfriend for buying one, or whether or not you have the right to influence her choices in this matter.
Simply put, in my opinion, this is something that you should not be pursuing. If you disapprove of your girlfriend’s choice, then you will have to decide whether it is significant enough of an issue for you to continue to pursue a relationship with her. If you are unsure of whether her clothing is immodest, then I can only recommend that you grant her the benefit of the doubt in making appropriate choices since this concerns women’s clothes (something with which, you, as a man, have no personal experience). In any case, I cannot recommend that you attempt discussing this matter with her. At this point in the relationship, her clothing choices are her business alone, and I’m afraid that you will appear to her to be an unsafe person if you comment on the alleged “transluscence” of her bikini bottom.
In short, you must respect your girlfriend’s personal autonomy as an adult human being to make her own choices in personal matters such as clothing. To do otherwise could mean taking the first step on a road that could lead in problematic directions.