Everyone knows the feeling of walking up to a piece of equipment, or a power rack, and seeing someone using it– It’s not the end of the world, but in most cases, it’s terribly inconvenient. In the unwritten rules of gym etiquette, you have the option of asking the person if you can “work in;” that is, perform your exercise while they are resting, then vice versa, and so on.
As part of this unwritten rule, that person has the option to decline you’re ability to work in with him, thus either derailing your workout, or delaying your workout. It’s generally frowned upon to not let people work in, but there is a case where it’s allowed–
I’m not going to try and work in with Ronnie Coleman when I’m squatting less than half than he is. Likewise, if someone is squatting less than half of what I squat, I decline them working in with me– The amount of time it would take to load and unload the plates will mess with my rest times. Unless you’re doing the same weight (or a similar weight), it’s a hassle to work in on some exercises. Of course, you can always ask, as there’s no harm in asking, but in this situation, I just patiently wait for the power rack to open up.
That’s a situation where it’s acceptable to decline. . . Is there a situation where it’s never okay to decline, though? Yes.
If you’re on a “selectorized” machine doing a single exercise, and you decline someone working in with you. . . That just means that you woke up that morning deciding to mess with people that day. (Side note: If you’re super setting on the same machine, that is the only time it’s acceptable to decline a work in on a selectorized machine.) There is no reason for you to not allow someone to work in– The amount of time it takes to change the setting is about 2 seconds, and the amount of time it takes to perform the exercise is well within anyone’s rest target.
While people will try and justify most other situations where you decline someone working in, most of them don’t really apply. Unless there’s a huge difference in weight lifted, or it’s something plate loaded (Barbells, Plate Loaded Machines), there’s no reason to decline a work in. (Unless they’re trying to be rude and take your stuff to the other side of the gym. In that case, decline, and tell them to adhere to “Wheaton’s Law.”)
If you’re not familiar with Wheaton’s Law, it’s important to live by in order to be a great citizen in the gym, and in life.