The problem is it is so easy to do. After flying four sectors my F/O and I were looking forward to a steak and beer on a HBA overnight, put it down to fatigue or over confidence or what ever, but I put in the worst landing of my career. I had recently changed types, (DC9 to B727) and think in my fatigue I reverted back to the old A/C. There is not a pilot alive who does not think at some point of his flying " oh ****,this is not going to be pretty" and it was'nt. The pax were fairly rattled, and turned their heads to see who the idiot was who tried to kill them,as they disambarked, and the F/O and F/E were very polite but obviously shaken. The LAME was less forgiving " You were fu$kin lucky you didnt get a fu%kin spar up your ar$e" and sign the heavy landing report! On the crew bus, I thought about it very hard, and remembered the F/O bracing himself for the landing, I asked him why he did not ask for a go around he replied " I never thought at any stage you would lose control of the A/C" which I didn't but I could have. We both agreed over a beer that we had committed a cardinal sin, I for not going around, he,for not requesting it, it was a big wakeup call for us both, and I have to say my confidence in my flying ability was tested. And that was a very good thing. I had to submit a report due to the heavy landing paper, and I fully expected to have to do a Sim but nothing more was said (other than the odd snide but humourous remarks from other pilots) (the Townsville refueler has a lot to answer for)! Fatigue played a big part in it, but to my shame,overconfidence also played a part, and I took that lesson with me for the rest of my career.