Just a quick vent

So my very pregnant friend and I were doing the school run (both nannies), and she starts telling me about some maternity clothes she got online that were a bit rubbish. A parent from the school joins in and starts talking about maternity clothes when she was pregnant, totally cutting across our conversation and essentially butting me out of it (TTC #1, so no Mat clothes experience). This isn't the first time someone who has children has taken over a conversation, something that actually wouldn't normally bug me. But because I desperately want to be in a situation to complain about maternity clothes, it really got to me. Of course I now that this other person has no idea what's going on in my life, and nothing is meant by it. I just think I'm more annoyed at myself for being annoyed. But.....I'm annoyed.