Ubuntu and Crunch bang Dual boot
 

I have crunch bang installed on my computer. How do I safely install ubuntu without messing up crunch bang. I used to have Ubuntu installed but when I installed crunch bang they both broke and I don't want that to happen again

You need separate partitions for the root file system. ie if you have Crunch on sda1 then put buntu on sda2, or what ever the next partition will be on the system.

Your /home partition may be ( or may not be ) safe to share. A lot depends on the desktops you plan on running on the systems. If they are the same desktop, sharing is possible. Watch the levels of each, you may cause problems from one to the other. It is safer to have separate /home partitions.

Swap can safely be shared.

Boot manager. Only one installation can manage your boot manager. I know buntu uses grub 2. Check into Crunch. Pick one, and only one to manage the booting of the system.

If you separate the partitions, and understand which one system manages the booting, you should be O.K.

Haven't looked at Crunchbang in a couple of years, so ...

As @camorri said, booting is usually the major hurdle. The installed system will "own" the MBR, and (by default) the new system will take it over. Generally problems don't appear till (much) later when the initial system updates the loader - and re-writes the MBR again. Then you lose access to the newer system altogether - although it's still there.
My favoured solution is to force new installations to install the bootloader to a partition (root usually these days) rather than the MBR. Grub2 complains, but works. Then go boot back to the original and add the new system to the boot menu - on Crunchbang it may be as easy as "update-grub".

And whilst you can share swap, any system that uses UUID to mount it will probably fail to boot if the (new) system being installed does a mkswap. Usually easiest to fix things like that from a liveCD after the problem shows up.