Maybe it's just jealousy, but I'm super sick of everyone commenting on how cool it is that my brother's girlfriend doesn't mind getting her hands dirty. Except she didn't start doing that until she got with my brother and I've been working in the garage since before I could drive. I just don't throw it in everyone's face. Also, if I break something, I fix it. She breaks everyone else's stuff and just leaves it for them to fix it. He had 2 nice cars and a nice 4 wheeler & she's wrecked all of them! I mention something to anyone other than my boyfriend and they just tell me I'm just jealous. NO, I just wish everyone would stop pumping up her ego and realize other girls can do exactly what she's doing. For example, there is a lady in town I don't get a long with. She has a "man's" job and you never hear about it. I just want to tell her & them to just shut up about it already. I can do everything she can do.
I see how that would be frustrating to have to deal with. Without knowing the situation first hand, it's hard to say exactly what's going on, so it could be one, some, or a combination of all of these:
First, if you've been getting your hands dirty and fixing things since before you could even drive, it's probably a skill everyone knows you can do by now. So it's not that people don't realize what you're doing or recognize your talent, it's just that they already know what you're capable of.
Your friends/family/etc. might also feel bad for your brother's girlfriend, because you are so good at fixing things, and all she seems to do is break things. Maybe they felt like they should try to be kind and make her feel better. Kind of an "A for effort" sort of thing.
I also think it's possible that it's less about boosting her confidence and more about boosting your brother's. Maybe people feel like they should find something to compliment her on to have something nice to say about her to your brother. I don't know the dynamic of the relationship, but maybe your brother has really fallen hard for her, so his friends don't want to let him down by pointing out negatives. Maybe they think it's cool that she has taken an interest in something that your brother seems very into, so the compliments aren't so much about how good she is at fixing things, but that she's making an effort at all.
Aside from those possibilities, it really could be any number of things - they could be trying to show the two of you that you have stuff in common and might be trying to bring you closer; maybe none of them are actually thinking about it when they say anything and it just seems like it's something that "everyone" says "all the time" because it bothers you so you pick up on it and notice it more than others. But at the end of the day, you could sit and think up all the possible scenarios that might possibly be going on, but that still won't fix anything. Just focus on your own time and ability fixing things and let your talent speak for itself. I'm sure soon it will start to settle down and no one will even think twice when they see your brother's girlfriend working and getting her hands dirty. Until then, just remember that a compliment to someone else is not an insult to you; other people's successes don't bring you down, so don't let this take you down! Wishing you all the best!