My building is getting security guards. They will be checking bags, so in the future they will be getting to see my pump, pump parts and milk every day. Tell me it is not as awkward as I feel it will be. I flew with a week of milk and it wasn't a big deal, but that was once and I didn't know anyone.
I'm willing to bet a pump and milk might not be the weirdest thing they see all day
Really though, the first day or two might be weird, then they're going to remember you and what's in the bag and you're going to be through security quickly. I can't imagine they'll going to ask you to take it out and show them how it works.
I vote might be weird the first day but will be totally fine after that. Think of all the things people carry in their bags - tampons, divacups, underwear - and remind yourself it's totally normal
ETA: I'm not saying the things I mentioned are weird, just that they're completely normal but yet might make someone feel slightly embarrassed at first!