I posted about this before - but I recall boarding a UA flight once, and a family of six (3 kidlets + grandma) were boarding as I strutted up to the priority line. The two parents had "gone through", but the gate agent held up her hand bruskly to stop the granny and three children and waved me over as though I were royalty. I thought that was incredibly rude of the gate agent and so I feel self conscious about late priority boarding with UA, just because the gate agents do it in such a brusk (for lack of the better word) fashion.