Farting

Flatulence or "farting" was a bodily process that affected some species, involving the expulsion of gas.

Many people thought farting humourous. (TV: Revenge of the Slitheen)

Amongst humans
Farting was frowned upon by humans, due to its foul smell and loud noise. Many humans, though, thought farting humourous. (TV: Revenge of the Slitheen) Ingestion of food such as cabbage, (TV: Revenge of the Slitheen) and baked beans, (TV: The Bounty Hunter) could induce it.

Among the Raxacoricofallapatorian species
When members of the Slitheen family used Compression fields to fit themselves into human skin suits, it caused a condition called "gas exchange" which was similar to farting but with a smell like bad breath. This was due to calcium decay as Raxacoricofallapatorians were a calcium-based species. (TV: Aliens of London / World War Three)

When Blon Fel-Fotch Passameer-Day Slitheen, in the form of Margaret Blaine, took Cathy Salt to the toilets to kill her, she noted her "little tummy" was "complaining" when she farted loudly. Soon after, when she farted after entering the toilet, Cathy remarked, "Sounds like we got here just in time.". (TV: Boom Town)

A Slitheen disguised as Ambassador Rahnius, who arrived in Sarah Jane Smith's attic to apparently reward her and friends, was exposed by his uncontrollable farting, despite blaming it on his chair. (TV: From Raxacoricofallapatorius with Love)

Leef Apple Glyn Slitheen-Blathereen farted while eating Shepherd's pie cooked by Clyde Langer. Later on, Sarah Jane had Mr Smith replicate the sound of an alarm bell to destroy the Rakweed in Leef and Tree's stomachs, causing a massive methane gas build-up which killed them both, exploding and covering Sarah Jane's attic with their remains. Clyde Langer noted that they had "farted themselves to death farting." (TV: The Gift)(TV: The Lost Boy)

Other instances
Farting was still possible after death, as the living dead man Owen Harper discovered shortly after being brought back to life by the resurrection gauntlet. He mourned in advance his last fart, saying that, along with sex, he'd miss it. (TV: Dead Man Walking)

The governor of Justicia's obesity and flatulence led Rose Tyler to believe he was a member of the Slitheen family in disguise. She attacked him, but soon discovered he was just a large human. (PROSE: The Monsters Inside)

When Victor Kennedy absorbed Bliss, her face ended up on his right buttock. When Elton Pope asked where she was, Kennedy lifted himself up, farting as Bliss told him he didn't want to know. (TV: Love & Monsters)

Having experienced a sudden bout of stomach trouble as part of the Adipose necklace-induced full parthenogenesis, Stacey Campbell suffered a loud fart on the moment of her death as she exploded into a pile of Adipose in her bathroom, which was witnessed by Donna Noble. (TV: Partners in Crime)

The living Mona Lisa painting claimed that her model "farted like a donkey." The animated painting also asserted that her so-called enigmatic smile was due to her model experiencing wind during the portrait sittings. (TV: Mona Lisa's Revenge)

The Vykoids disguised their ship as a mammoth which, as encountered by Amy Pond and the Eleventh Doctor, was notorious for its farting. (PROSE: The Forgotten Army)

Other references
Clyde Langer commented to Maria Jackson that the claim of what were apparently Luke Smith's real parents "[stank] like a Christmas dinner fart". (TV: The Lost Boy) Among the jokes he told in order to use laughter to defeat the Pied Piper was "What's invisible and smells like carrots? Rabbit farts." (TV: The Day of the Clown) Clyde later commented that an old shed next to Ashen Hill Manor smelt like "cucumber farts". (TV: The Eternity Trap)