S.A.M. gets an honorable mention because either I can't hit the plane or I hit it and I get ran over by the burnt chassis half second after.
Are you shooting from the runway? Because generally I stay on the lower level just beneath and shoot from there.
If I'm looking to be thorough and complete all of the Donald Love missions, Escort Service can be pretty damned irritating. Having to run interference on all the Cartel Cruisers plus trying to stay ahead of the van to take out the gunmen can be a real pain.
I take back what I said. I finished III's campaign some days ago and S.A.M. was incredibly easy (at least the part where I had to shoot down the plane. I kept repeating it because the damn FBI kept killing me). I guess that when I was a kid I simply didn't try spamming the rocket launcher until the plane explode.
I think the worst mission now for me has to be Uzi Rider. I have to take this slow ass POS car, drive aaaaaaaall the way to Portland, make a gang that I like dislike me, while I'm working for a gang that I know is gonna betray me a couple of missions later. Then drive aaaaaaaall the way back to Staunton, still in the crappy car. Yeah, no. I even failed twice when I was about to finish the mission. I hit the edge of the sidewalk and, somehow, the damn car ended up on it's roof and I failed the mission. I was so pissed. The second time I simply took a sharp turn and the stupid car ended upside down again. It's like a small version of the Ambulance.
f*ck this mission.