Is this one rule for one, one for another?

Now and again I have often inadvertently said comments to my girlfriend where she has said "don't be crass , I don't like it. Please don't do it again ".
It may have been a sexual remark or regarding her figure or something I mean no harm and try to be better, although now and then I slip.
Recently a friend of hers (a guy) on social media made a couple of comments about her breasts on social media . She has known him for a good few years (I've been with her 8 months). When I told her I didn't appreciate his comments she said not to reply as it would embarrass her. She said it's only a harmless remark and means nothing. Is this double standards? How are his remarks ok but mine are crass?

Yes, it sounds like a double standard to me, but it could be that she just doens't want to start any drama on social media. Personally, I would probably let the remark slide myself rather than cause a scene, but it would be nice if she made a private comment to him that she didn't appreciate the comment. I do agree that it's not for you to comment on. Just saying less drama is a good thing.

It's a bit of a tricky situation. I don't know - I'm just putting it out there; maybe she'll genuinely be embarrassed if you said something ..... maybe put the ball in her court .... and ask her if she can send him a private message to not publicly make such remarks about her appearance as you do not find this tasteful (if, of course, she agrees to do this)?

The last thing I want to do is to make her uncomfortable. But I'd she is not taking my feelings into account. I'm insecure anyway. If she is only taking her friends feelings into account and not mine surely that's wrong. I don't ask to be put above her friends bit surely I should be on a par with them?
If I'm unaware of saying anything crass in future but am accused of crassness, would I be wrong to ask why it is ok for her friend to be crass but not me? I certainly mean no harm or disrespect

Personally it sounds like she likes the attention from him. It's not a double standard in so much as she like the "crass comments" (I call it flirting) from him, but not so much you. I would suggest avoiding her social media if I were you.

Social media is terrible for relationships anyway.

She is insecure herself and I agree she likes the attention not that she'd act on it I think but as an insecure person myself it really doesn't help

Yes, I agree.

I think that this is the most important statement here:

"But she is not taking my feelings into account."

Honestly?

I believe that she should be and this should come into the conversation that you have with her. Relationships require comittment from both parties, not just one.

I have no idea where your girlfriend is coming from in this situation but I can give you one explanation that is something I might do.

Whether or not I say something to a guy friend depends on my mood and how offensive I found the comment.

If I'm dating a guy I try to always tell him if I find a sexual/ized comment offensive. Why? I'm not having sex with my guy friend. I'm not looking for intimacy or to trust my guy friend on that level. Sure, I want my guy friend to have a clue but I won't always say something everytime because I might not mind some guy that is just a friend says gross stuff. I might even find my gross male friend funny.

So, yes, I have a double standard but that double standard is based on expectation. I expect that guy I'm dating to respect my body (and mind and me his) and I want to think of my guy as someone that respects the mind/body of women.
In a weird way, it may be a compliment. She may expect more from you.

It may be that what your girlfriend expects of a partner is more than what she expects of a casual friend. I'll bet she didn't particularly enjoy the friend's remark. But she doesn't want to make an issue of it. With you she is more comfortable in being very open about what bothers her. I think you might consider taking the double standard as a tribute to your relationship being far more special than any other relationship in her life. She wants to keep it that way.

I agree with the last couple of comments, it might be a sign of strength in your relationship that she can be open with you, maybe she doesn't have that amount of trust in her friend. You could talk it through with her, try not to jump to conclusions about her motivations.

Thanks to you all. I admit to looking too closely and seeing problems where they perhaps don't exist. I won't make an issue of it. In case it persists or becomes a regular thing I may address it again, however I don't want to cause stress in our relationship