I have to disagree with Max. I have found that most "people" on this planet are decent folks - ground agents and flight attendants included. I try to treat everyone nicely and it is a rare occasion when I run into anyone nasty. I think good folks are in the majority but very quiet about it. It is the horrible encounters that one remembers most,unfortunately, and this does tend to colour attitudes. As for the trials and tribulations of crowded airports,flights, delays etc. I try to step back mentally and observe - makes it less personal and "Turned out nice again, didn't it?"
As for LHR T3 - absolutely horrible terminal. As a non-EU resident flying into it six times a year over many years - I have never, ever had to queue longer than five minutes at customs and immigration. Never had a lost bag either. Damn charmed life...so far.