The worst I've come across are pilots who have a 1 year or 2 on a fresh commercial, they know it all and spray out calls as quick as they can. Bad radio calls are covered by every form of flying, from students through to an odd airline pilot, most are professionals and treat it as such.
We've all heard (or half heard) a 2 stroke ultralight of some sort where an un-shielded ignition makes the transmission unreadable. Or gliders where their battery is running on 3 volts and the transmission is almost inaudible, some areas gliders have a reputation for not talking at all (Also IFR but that's for another thread). Goes right through from machine gun transmissions from mail run pilots to the odd smug rookie talking down to everybody in a regional airliner.
We all have to try and make our calls understandable. No need to try and complicate with all sorts of terms and procedure. Just tell people where you are and your intentions in the simplest of terms.
Example: "5 miles Southwest 3000 inbound". Also no need to give a highly detailed rundown on your circuit joining just what leg and if not standard then just a wide or close, another example: "Joining a close downwind low level for 03"
No need to say nautical miles, that's what we work in, we all know that. Also no need to say "This time" after every transmission, we all know what the time is, it's just wasted bandwidth.