Arse
Definition 1 of 3
Pro Tip 1/3
Informal Slang
Arse is very informal and often considered rude; use in casual settings only. Oops, I've just texted my boss 'Arse over tit', that was inappropriate.
Pro Tip 2/3
Not for Formality
Avoid 'arse' in formal writing or speaking, instead use 'buttocks' or 'rear end'. In the medical report, he wrote 'buttocks' instead of 'arse'.
Pro Tip 3/3
Humorous Insult
Used jokingly among friends, but can offend if the relationship isn't close. My mates laughed when I said, 'I fell on my arse'.