I've noticed three classes of bad English. The apologetic folk, who will often try to explain things in multiple ways, or be extra-verbose, in an effort to get their point across clearly. Second, the unapologetically bad folk, who write a semi-incoherent sentence and respond poorly to requests for clarification (often simply repeating the same sentence). Third, the lazy native (or fluent) speaker. This is an entirely new class of errors, which is easy enough to read through (being native and lazy myself), but sends a strong signal that I shouldn't place too much importance on what I'm reading.