I know the feeling.
When I was training it was at a military field.The ATC guys used to pop in the club for a chat now and then.
I was talking to one of them one day about the `Brain Lock Out`, just after hitting the button.He told me,`Remember just to tell us, who you are,where you are and what you want.If there is anything else we will ask you".This helped me get over the phobia of the button and has been quoted to other students and pilots in the same boat.
Hope its a little help,but we have all come across a controller with the hump,we are all human after all,even controllers,its a matter of `Tact` on their part as in the case of Thames Radar very helpful.