Maybe, but certainly not much
When you take a shower, you're mixing a combination of hot and cold water to make a comfortable temperature for the shower water. A toilet draws only off the cold water system. In older or poorly designed plumbing systems, when you flush the toilet, the cold water is pulled by toilet, so the water coming through the shower is only drawing from the hot water tank.
Because it effects the water pressure of the shower. This causes the temperature of the water in the shower to also change.
One of the easiest and least expensive fixes for this problem is to adjust the flow of water into the toilet. If the toilet fills more slowly, it will not alter the water pressure enough to change the temperature of the shower. Another possible solution, which would require the purchase of a special valve and possibly installation by a plumber, is to install a thermostat-controlled water valve in the shower to keep the water flow at a constant temperature.
Because someone is using water somewhere else. For instance, if you are having a shower and someone flushes the toilet, the water going to the shower is decreased because some is going to the toilet now.
Because the two pipes are connected, and the shower is farther down the line than the toilet. So when you flush, you are hearing the water from the toilet pass by your tub. This is also why you will have sewage in your tub if your waste water line is extremely backed up.
Incorrect pipe size installations
1}drink 2}toilet 3}shower
Your drain line is plugged somewhere after your shower and toilet line are connected. The reason for the gurgle in your toilet is because air is trapped in the drain and your toilet is the closest place for air to flow to. If you had a vent on your toilet trap arm then it would gurgle in the vent rather in your toilet but your drain is still plugged and needs to be snaked out and maybe your drain line needs to be examined for right grade or broken.
This is not an uusual as when the toilet is flushed more cold water is drawn usually from the cold water pipe that suplies the shower with cold water so generaly the water under the shower gets hotter. The only way to stop this from happening is to lay an extra pipe all the way to the ater suply point, or fit a pump to maintain the presure
Not advisable ... water is a conductor of electricity, so if a lightening bolt makes contact with the water lines in a home or apartment, and a person is in the shower with the water running, they are apt to get fried.
A toilet. Same reason a shower is called a rain locker
Anything connected to water pipes. Sink, faucet, toilet, shower and controls.