What is the relationship like between your DP/DH and your DM?
DP and I had our fair share of problems when we were younger but are in a place where we have 1 DS, a happy home and a lot of love for each other. Neither of us are perfect, sometimes I'm a bit selfish and sometimes he's a bit immature, but they don't extend past normal relationship problems and we have very good communication and an overall extremely happy relationship.
I just always get the feeling that DM doesn't like DP. She makes comments about how she didn't see me with someone like him. We've just had a conversation where she's invited me to hers at the weekend and I've said I'll ask DP and she's made a sarcastic comment about 'he'd love if you asked him permission, that's just what he's like'. It was supposed to be jokey but it annoyed me (for the record, I was asking because he's working late one night and not sure about the other and I want to check if he has the energy to look after our toddler after doing long days all week, I think it's just polite in a relationship, he'd never make things difficult!) 
But I also get the feeling when DP is home and DM is round that he doesn't like her either. He's usually so bubbly and jokey at home but as soon as DM is here he's very serious and doesn't say much and isn't his usual jokey self. He also makes comments about how I never treat her as shit as she treats me sometimes when she's on a rant, and occasionally makes a subtle comment about her being selfish etc (never explicitly but it's implied!).
AIBU for this to really bother me? They both make a solid effort to get on with each other and speak highly of each other (3/4 of the time), but it's the feeling of being in the same room as both of them and the subtle and snide comments from both of them (DM is worse than DP for it!). Do I just need to get over myself?