The complaints are usually from women talking about faster male runners revving up the treadmill to 10mph, sweating profusely all over the machine, staring at women while they run intensely, making hand gestures in the air like they are celebrating the finish line of a race they just won, etc.
If you are one of these types of people at your gym, try to be more modest when you run at a quicker pace on the treadmill. Cut all the histrionics.