Practice Pan X 3 make me furious to be honest. Chose another parallel frequency for these calls.
Whether you like it or not, it's perfectly correct use of 121.5 in UK airspace.
If something like this really does make you furious, I suggest you take advice from a aviation medical practitioner, because it sounds like you aren't coping too well with what is a fairly normal situation.
Alternatively, simply deselect the frequency at critical times and switch it back on a few seconds later when other people have finished talking.