One guy used to drive me crazy at my local gym. We were often there at the same time and he had this little superset type thing going where he would do squats and then grab some dumbbells close by and do presses and then go back to the squat rack, repeat etc. Except he always draped a towel on the rack to occupy it so he could easily return and do more squats. He'd be there for ages.
It drove me crazy and one day I got fed up and moved his towel and adjusted the squat settings so I could do my sets. He didn't like it, but I had to tell him that you just can't do that at busy times. See some other things that you might want to note when working out.
---> Gym Best Practices