What bothers me most are
A. Human builders who move the base while we're under attack/ decon turrets to "Reposition" just before a rush... especially if someone shouts "INC!!!"
B. Alien builders who build a crappy ground base. At S2 or higher, the aliens should never have their entire base at one point nor rely on defenses.
C. Aliens who "defend" the base by feeding. A lucisuit against a dretchstorm wins. Always. Sure, this is impertinent, but it's the same point: Bases with weak defenders may as well have noob builders. They usually do.