grouch — to be sulky or morose; show discontent; complain, especially in an irritable way.
bear — If you bear something somewhere, you carry it there or take it there.
belly-aching — Informal. a pain in the abdomen or bowels.
bug — A bug is an insect or similar small creature.
complainer — A complainer is someone who complains a lot about their problems or about things they do not like.
crab — A crab is a sea creature with a flat round body covered by a shell, and five pairs of legs with large claws on the front pair. Crabs usually move sideways.
crank — If you call someone a crank, you think their ideas or behaviour are strange.
mutter — to utter words indistinctly or in a low tone, often as if talking to oneself; murmur.
sorehead — a disgruntled or vindictive person, especially an unsportsmanlike loser: Don't be such a sorehead, they won fair and square.
sourpuss — a person having a grouchy disposition that is often accompanied by a scowling facial expression.
whiner — to utter a low, usually nasal, complaining cry or sound, as from uneasiness, discontent, peevishness, etc.: The puppies were whining from hunger.
griper — Informal. to complain naggingly or constantly; grumble.
grouser — to grumble; complain: I've never met anyone who grouses so much about his work.