You give no context, you give no reason, you give no example - try doing a 6 sector day in NE when your already late off chocks and there is a 20 min slot delay and your already trying to think of ways to make up time..... we're only human!
Human, yes. But professional to be transferred to a new frequency and begin transmitting the second you switch over, no.
I've been in that position you describe many times, and never have I found waiting a couple seconds to make sure I'm not breaking into the middle of a conversation has resulted in my not getting what I want. Normally, such an attitude results in someone else being inconvenienced.
Case in point: I once saw an aircraft have to go around after being told to expect a late landing clearance. As they were about a mile back, some joker joins the frequency and tells his life story - including lots of "ums" and "ahs." This lasted so long that the guys had to go around because they didn't get the clearance in time.
A little bit of professionalism can go a long way.