One of the best and most addicting forms of competition consisting of swimming, cycling, and running all at varying degrees of distances. Triathlon is not for the weak, for it puts the athlete in an undescribeable amount of pain, but when the race is over, you want to do it again. Anyone who downplays the difficulty of a triathlon or the classification of it as a sport should be beaten.
I did my first triathlon last summer, and I have since been addicted.
Any night of sexual activity consisting of the entire trifecta of penetrating sexual acts. The official order consist of oral, vaginal, and finally anal sex. However, if used as "we might as well have pulled a triathlon" it's understood the acts were there, but not the order.
A reverse triathlon would simply be the acts in reverse order.
If I really like the guy I let him run the triathlon on me, but no one is going backwards on me, that's just dirty.