Ah, darning a sock! That's easy. Maybe even too easy. I can go bigger! How about using this old rainbow embroidery thread on these here jeans? Make some fabulous knee patches!
... I may have gone a little overboard. I have to take a break now because you don't shove away an 18 year old cat who wants cuddles. Will post another picture when it's finished, maybe tomorrow.
I'm thinking the darn will last longer if you weave it into the pants, too, not just into the yarn that's attached to the pants....I don't know if I worded that right. When you weave, weave not just through your yarn, but poke down through the pants and back up with each weave, too. This helps distribute the tension when you wear the pants, making it less likely to cause a new hole where you attached the yarn to the pants.
Tried a couple styles of darning/mending holes. “Real” darning on a kitchen towel that I wanted to make sure stayed flat, and the quick and easy ladder stitch style on my favourite sleep shirt that got eaten by the dryer. The loose fit and pattern will help hide the puckering from that method.