The water pressure in my main shower has been absolute garbage for months because the cheap plastic shower head was completely clogged up with white limescale buildup. It finally got so bad that water was barely shooting out of half the holes, so I bought a basic chrome replacement at the store. I thought it would be a simple two minute job where you just unscrew the old one by hand and twist the new one on. What an absolute nightmare.
The old fixture was basically welded onto the metal pipe from years of hard water corrosion. I tried twisting it with my bare hands and the whole pipe inside the wall started creaking and flexing dangerously, which completely freaked me out. I had to run to the garage to find two separate pairs of pliers just to hold the main wall pipe perfectly still while I practically threw my whole weight against the old shower head to break the crusty seal loose. When it finally popped off, a bunch of gross, gray water leaked straight down my sleeve.
Then came the real headache of getting the new chrome piece to seal without dripping. The first time I screwed it on and turned the shower taps back on, water started spraying out in a steady mist right from the connection threads and soaking the ceiling drywall. I had to shut it down, unscrew the whole thing again, scrape off the old decayed pipe tape with a pocket knife, and wrap the threads in about six layers of fresh Teflon tape.
It is twisted on tightly now and the new spray settings work fine without any leaking from the base. The water pressure is actually back to normal, but now I have to go deal with a massive puddle on the bathroom floor because I forgot to pull the shower curtain closed before testing the water.