Messr. Padfoot occasionally acknowledges that he is not, in fact, perfect. He knows of his (few) faults, knows knows he has a short temper with a short fuse and that he can say hurtful things that he may or may not mean. This, of course, does not apply to any dealings involving Snivellus. Slimey git deserved every bit of what he got.
Unfortunately, Messr. Padfoot's anger is usually directed at one of several targets- Messr. Prongs (who has learned, by now, to fight back, that these words are never meant), Messr. Wormtail (he just grates on one sometimes, honestly...), Snivellus, or Messr. Moony.
The times with Moony are the worst, but not always completely unprovoked. Messr. Padfoot realizes, though, that it takes two to tango, and that neither of them is completely to blame.
Messr. Padfoot never knows how to apologize, either. Messr. Moony no longer caves in to a charming smile and grovelled apologies (something only done in the most dire of situations). Words are hollow, gestures are cliche and overdone. Messr. Padfoot also wonders why apology words mean nothing, but impassioned ones can be held against one for a dreadfully long time.
Messr. Moony is the only one who can make him feel like stabbing his wand through his own chest.
Messr. Padfoot hopes he knows this, and knows that he is sorry.
Remus Lupin put down the Marauder's Map with the writing that had appeared the instant he picked it up, and went to go find Sirius.