Mulder spent his time quite well on the flight between the US and Russia.
He read an article on the lush natural wonders of Sri Lanka and thought of retiring there.
He did a crossword puzzle. Then he redid the crossword puzzle using porn words.
He skimmed over the airplane safety instructions, replacing words in his head every so often - in case of evacuation, steal Krycek's floatation device.
Finally he took out a pencil and pad and started writing down ideas on how to kill Krycek. He also made especially sure that Krycek saw what he was doing.
1. Shoot him.
2. Hang him.
3. Train a monkey to eat his brains out.
4. Engage in years and years of psychological torture until he kills himself.
...and on and on.
Krycek, who had now gotten tired of flirting with the flight attendant in exchange for more vodka, turned his attention to Mulder. He leant over a bit to read.
"I was running out of ideas!"
Krycek smiled. "Autoerotic asphyxiation."