If you're overtaking, you're supposed to speed up. If speeding up would put you at an unsafe speed, then overtaking is too dangerous at that moment. If there isn't enough difference in speed to overtake in a timely manner, there isn't enough difference in speed you should want to overtake.

Just because cruise control makes you drive a constant speed doesn't mean it makes you drive the correct speed. Either adjust it down and accept your place in traffic, or turn it off long enough to speed up and complete your overtake without turning your two-ton death machine into an obstacle for everyone else to maneuver around.

fuck them lol in a rush for nothing

First of all, you don't know that. They could be having an emergency. If it was your relative dying at the hospital, you'd want people to move out of your way too. Second of all, it's not your job to police the roads. It's not your job to make sure people drive slow enough. If you think someone is being dangerous by driving too fast, the safest thing you can do is get the fuck out of their way. Adding another car to an already dangerous situation only makes the situation more dangerous.

Call and report them if tou have to, but don't try to enforce the law, that's not your job.