As far as I'm concerned, the radio is a safety tool first, and a means to communicate with ATC second. That means that if there's a direct safety issue, I'm going to talk to the relevant aircraft directly, instead of indirectly letting ATC know that I'm not happy about the situation and hoping they're going to do something about it.
"Dornier blah blah blah, this is a student pilot in G-ABCD, get away from me please." or something more strongly worded.