This is a video of astronomer Scott Manley discussing how much energy it would take something like the Death Star to blow up a planet. Apparently to blow up an earth-like planet it would take something like 3 trillion trillion trillion Joules. For reference, a lightning bolt carries about five billion joules of energy, so it would take a lot of lightning bolts. I haven't done the math yet to see how that translates into laser pointers, but I have eleven taped together so far. Prepare to die, earth!
Keep going for the video and get your math and science on.
Thanks to Allesandro, who agrees the best way to kill a planet is to keep doing whatever the hell we're doing. It might not be the fastest, but it's definitely working.