The easiest example here is a computer/laptop... e.g. when the CD-ROM is spinning when you are perhaps playing a movie, the kinetic energy causes friction, which results in heat. All computers need a fan to prevent them over-heating for this very reason. Therefore heat is lost and energy is wasted.
Another example is a lightbulb. When a light is switched on and left for a long time, the current flowing through the filament (the thin bit of wire in the bulb) causes heating (due to electron-ion collisions but you may not need to know that) so energy is wasted as thermal energy instead of light energy.
These are just a few examples but other ones you could use are tv screens, kettles, toasters, etc :)
