When I was taking apart the tiny, neglected LeMond I bought last winter, the cheap plastic pedals were rusted on there pretty damn solid. being a patient man, I applied some PB blaster and did a lot of tapping on the crank and spindle, then repeated that three or four days in a row. One pedal finally broke free, but the other one stripped under the weight of a fat caveman leaning on a 15mm wrench with a persuader bar.

What to do? I didn't want to just toss a decent Tri-Color crank set just because some dingus forgot to lube the pedal spindle before screwing it in.

What eventually worked was disassembling the pedal from the outside in, leaving just the spindle in place, and then breaking that out with a 24" pipewrench. Last resort type stuff, but it worked.