Get A Grip:
Sometimes the easiest answer is the best. Often you can get stuck ferrules apart just by getting a better grip on the sections than your bare hands will provide, especially on cold, damp days or in the sweaty, humid days of summer.
It's a good idea to carry a couple of small pieces of rubber with you in your fishing bag or vest. A few smaller pieces from a bicycle tire inner tube (or from an inner tube repair kit) will work great for this, as it allows you to really increase the power of your grip on the rod sections without marking or marring the rod. In the rod shop, I will typically use a couple of latex gloves - the same kind I use for other jobs like gluing up a rod or varnishing. The latex gloves aren't as strong as the rubber & will easily tare, but they often do the trick for me & I always have a supply of them in the shop. Just be sure to remember the old rule about assembling & breaking down a rod: "rod together, hands together; rod apart, hands apart".
If the old rubber trick doesn't work for you, then you can increase your pulling power by asking someone to help you. The two of you stand facing each other, each grasping a rod section. Each of you pulls on their section of the rod as if the two of you were playing a game of 'tug of war'. Just make sure that you both pull the rod sections straight apart!! It also helps if you each grasp your rod section near the ferrules. If you bend the rod too much as you're putting all that pressure on it, bad things cold happen; and for goodness sake don't stab yourself with the rod section when it does come apart - you're having a bad enough time already without becoming the talk of the local emergency room (that's a joke, I hope). Don't be afraid to really pull on the rod, though - both of you - as you're starting to run low on options.
If both of the previous suggestions haven't worked out for you (& they usually do) all is not lost - even though it may seem like it is. Now we're going to move onto an advanced, but simple, trick for getting those nasty ferrules apart. To do this, we're going to have to leave the rod together for a while - preferably in an upright position or at least horizontal. We're going to apply a little science.
Take a source of soft heat & gently apply it to the female ferrule only (& only the ferrule, not any of the surrounding bamboo). An alcohol lamp is best but a lighter or even a candle will do in a pinch. Be very careful using a heat gun - keep the rod a fair distance away from the gun on it's lowest setting. You don't want to heat the ferrule up so much that touching it will burn you, but do get it hot enough where you can hold it in your hand for about 3 to 5 seconds before it gets too hot to hold.
Once you have the female ferrule hot enough, apply some penetrating oil to the welt, or lip, of the ferrule - right where the male & female ferrules meet. What you're attempting to do is expand the female ferrule ever so slightly (micro-thousandths of an inch) - just enough for the oil to creep & leach down in between the two. Now let it sit for a few hours - over night is even better. If the oil got down in there your rod should come apart now.
Most of time proper rod maintenance will keep the ferrules from ever sticking in the first place. This isn't hard & takes only a few seconds every time you fish the rod. Simply wipe them down with a soft, dry rag when you're done fishing each time & don't store the rod away for extended periods with the ferrules together. Once a year (or more often) clean them up with some rubbing alcohol - both the male slide & the inside of the female. Some folks lubricate their ferrules with mild bar soap or beeswax. If, or when, I lubricate ferrules I prefer pure beeswax as it seems to last longer, doesn't harm the metal, & works a little better in my opinion.
So if the ferrules on your bamboo rod should not want to come apart for you, you don't need to cuss (though you might) or worry (though you probably will). Just follow the suggestions above & you should be just fine.