The comprehensive rules on taking shortcuts in Magic, as per your request. (Sorry, long...)
If you refuse to take a shortcut out of an infinite loop when you have the opportunity, you are committing deliberate timewasting as Andrey's answer suggests; a definite no-no in a tournament, and hopefully in a friendly group as well!
- Taking Shortcuts
715.1. When playing a game, players typically make use of mutually
understood shortcuts rather than explicitly identifying each game
choice (either taking an action or passing priority) a player makes.
715.1a The rules for taking shortcuts are largely unformalized. As
long as each player in the game understands the intent of each other
player, any shortcut system they use is acceptable.
715.1b Occasionally the game gets into a state in which a set of
actions could be repeated indefinitely (thus creating a "loop"). In
that case, the shortcut rules can be used to determine how many times
those actions are repeated without having to actually perform them,
and how the loop is broken.
715.2. Taking a shortcut follows the following procedure.
715.2a At any point in the game, the player with priority may suggest
a shortcut by describing a sequence of game choices, for all players,
that may be legally taken based on the current game state and the
predictable results of the sequence of choices. This sequence may be a
non-repetitive series of choices, a loop that repeats a specified
number of times, multiple loops, or nested loops, and may even cross
multiple turns. It can't include conditional actions, where the
outcome of a game event determines the next action a player takes. The
ending point of this sequence must be a place where a player has
priority, though it need not be the player proposing the shortcut.
Example: A player controls a creature enchanted by Presence of Gond,
which grants the creature the ability "{T}: Put a 1/1 green Elf
Warrior creature token onto the battlefield," and another player
controls Intruder Alarm, which reads, in part, "Whenever a creature
enters the battlefield, untap all creatures." When the player has
priority, he may suggest "I'll create a million tokens," indicating
the sequence of activating the creature's ability, all players passing
priority, letting the creature's ability resolve and put a token onto
the battlefield (which causes Intruder Alarm's ability to trigger),
Intruder Alarm's controller putting that triggered ability on the
stack, all players passing priority, Intruder Alarm's triggered
ability resolving, all players passing priority until the player
proposing the shortcut has priority, and repeating that sequence
999,999 more times, ending just after the last token-creating ability
resolves.
715.2b Each other player, in turn order starting after the player who
suggested the shortcut, may either accept the proposed sequence, or
shorten it by naming a place where he or she will make a game choice
that's different than what's been proposed. (The player doesn't need
to specify at this time what the new choice will be.) This place
becomes the new ending point of the proposed sequence. Example: The
active player draws a card during her draw step, then says, "Go." The
nonactive player is holding Into the Fray (an instant that says
"Target creature attacks this turn if able") and says, "I'd like to
cast a spell during your beginning of combat step." The current
proposed shortcut is that all players pass priority at all
opportunities during the turn until the nonactive player has priority
during the beginning of combat step.
715.2c Once the last player has either accepted or shortened the
shortcut proposal, the shortcut is taken. The game advances to the
last proposed ending point, with all game choices contained in the
shortcut proposal having been taken. If the shortcut was shortened
from the original proposal, the player who now has priority must make
a different game choice than what was originally proposed for that
player.
715.3. Sometimes a loop can be fragmented, meaning that each player
involved in the loop performs an independent action that results in
the same game state being reached multiple times. If that happens, the
active player (or, if the active player is not involved in the loop,
the first player in turn order who is involved) must then make a
different game choice so the loop does not continue. Example: In a
two-player game, the active player controls a creature with the
ability "{0}: [This creature] gains flying," the nonactive player
controls a permanent with the ability "{0}: Target creature loses
flying," and nothing in the game cares how many times an ability has
been activated. Say the active player activates his creature's
ability, it resolves, then the nonactive player activates her
permanent's ability targeting that creature, and it resolves. This
returns the game to a game state it was at before. The active player
must make a different game choice (in other words, anything other than
activating that creature's ability again). The creature doesn't have
flying. Note that the nonactive player could have prevented the
fragmented loop simply by not activating her permanent's ability, in
which case the creature would have had flying. The nonactive player
always has the final choice and is therefore able to determine whether
the creature has flying.
715.4. If a loop contains only mandatory actions, the game is a draw.
(See rules 104.4b and 104.4f.)
715.5. No player can be forced to perform an action that would end a
loop other than actions called for by objects involved in the loop.
Example: A player controls Seal of Cleansing, an enchantment that
reads, "Sacrifice Seal of Cleansing: Destroy target artifact or
enchantment." A mandatory loop that involves an artifact begins. The
player is not forced to sacrifice Seal of Cleansing to destroy the
artifact and end the loop.
715.6. If a loop contains an effect that says "[A] unless [B]," where
[A] and [B] are each actions, no player can be forced to perform [B]
to break the loop. If no player chooses to perform [B], the loop will
continue as though [A] were mandatory.
Door to nothingnessyou still lose the game.