In diving, you generally dive with a dive buddy. Before descending into the deep, it's highly reccommended that you and your buddy do a buddy check, to ensure you've both remembered to assemble your equipment correctly, and to familiarise yourself with your dive buddy's equipment. If you're diving on your own, you're often assigned a buddy for a particular dive by the dive operator - so the buddy check might be the first time you see a particular type of buoyancy control device or similar.
The check itself follows the BWRAF model. A lot of acronyms have been made up to remember this model, some popular ones are "Bruce Willis Ruins All Films", "Bangkok Women Really Are Fellas", "Begin With Review And Friend" or "Bring Weed, Rizlas And Fags". Less salubrious versions (such as "Big Women Require Anal Fisting") are also used - just not in front of paying customers.
The buddy check
B - Buyoyancy Control Device (BCD). It is meant to keep you neutrally buoyant at depth, or positively buoyant at the surface. The checks include making sure that the power inflator (usually powered by pressure from the scuba cylinder) works, that the deflator works, that the overpressure purge valves work, and that the oral inflator works properly. Finally, especially if you are using rented equipment you may be unfamiliar with - check that you know where the dump valves are, and that they are functioning as expected.
W - Weight system. If your buddy uses an integrated weight system, check that you know how to release it. If they use a weight-belt, it should be right-hand release, and free from the BCD itself, so it can be released in an emergency
R - Releases. In case of an emergency, you may have to take your (possibly unconscious) buddy out of their BCD. Be sure you know where their quick-releases are, and how they work. Ensure that you move your hands to each release; through repetition, you'll know what to do in case of an emergency. Remember to check their main tank strap, and a safety strap, if their BCD has one.
A - Air. Check that your buddy's air is fully turned on. Smell your own air to ensure it doesn't smell of diesel or paint fumes - or of anything you don't want to breathe, really. Once you're satisfied with the smell, 'taste' it, to ensure it tastes either perfectly clean, or slightly of rubber (the hoses are rubber, so that bit is generally unavoidable). Check your SPG (Submersible pressure gauge), to ensure you have enough air to complete the dive, and look at your SPG whilst you are breathing from your regulator, and your buddy is breathing from your alternate regulator. The purpose of this is to ensure that you know your system can sustain both of you breathing from your tank if necessary. Whilst breathing your SPG needle shouldn't move - if it does, your air might not be fully turned on, or there might be a problem with the regulator or the SPG itself.
F - Final check. Do you have your mask, snorkel and fins? If you are using a computer, do you have it with you, is it working, and do you know how to use it? If you are using an analogue depth gauge, did you remember to reset it? Finally, take a good look at your buddy fully kitted out so you can recognise them under the water. All OK? Time to go diving!