in two games, just this week, my opponent made a tactical mistake, i took advantage of the tactical mistake and then my opponent would either leave the game or let their flag fall.
thanks to lichess, when a player abandons the game, the player who stays can claim victory. those situations aren't so painful. i remember when i was actively playing on FICS, that unless both players had a certain variable turned on (i think it was "noescape"), if one player abandoned the game, the game would go into this limbo status where neither one could claim victory, unless the other ceded the game. and if you wanted to claim the victory, you had to message the other player or contact the server admin - painful.
but then there is another class of sore loser - those who let their flag fall. let me respectfully say "screw you" to those who are in a losing position and intentionally let their flag fall rather than resigning or even abandoning the game. every single player who does this is automatically added to my block list. i know, that doesn't sound so revengeful, but it gives me a certain degree of satisfaction.