Context also helps: this is from the wonderful late-80's film, "UHF," starring the incomparable Weird Al Yankovik and Michael Richards.
Some goons are ransacking the TV station, IIRC, and they happen upon this supposed janitorial, or "Supplies" closet. Expecting to find a nice save point or some epic loot to aid them on their raid, they open the "supplies" door. Much to their dismay, however, they are assaulted by a team of rogue Japanese martial arts experts and, achieving a +4 to offense from their rallying call, the ninjas descend upon the hapless corporate raiders.
Let it be known that they were fairly warned...
Hollywood Lessons:
1. It does not matter if you are heavily outnumbered in a fight involving martial arts: your enemies will wait patiently to attack you one by one, dancing around in a threatening manner until you have knocked out their predecessors.
2. Honest and hard-working policemen are traditionally gunned down three days before their retirement.
3. All beds have special L-shaped sheets that reach the armpit level of a woman, but only the waist level of the man lying beside her.
4. At least one of a pair of identical twins is born evil.
5. Most laptop computers are powerful enough to override the communications system of any invading alien society.
6. All grocery bags contain at least one stick of French bread.
7. Rather than wasting bullets, megalomaniacs prefer to kill their arch enemies using complicated machinery involving fuses, pulley systems, deadly gasses, lasers, and man-eating sharks, which will allow their captives at least a half-hour to escape.
8. You're very likely to survive any battle in any war unless you make the mistake of showing someone a picture of your sweetheart back home.
9. A man will show no pain while taking the most ferocious beating, but will wince when a woman tries to clean his wounds.
10. If a large pane of glass is visible, someone will be thrown through it before long.
11. If staying in a haunted house, women should investigate any strange noises in their most revealing underwear.
12. Even when driving down a perfectly straight road, it is necessary to turn the steering wheel vigorously from left to right every few moments.
13. All bombs are fitted with electronic timing devices with large red readouts so you know exactly when they're going to go off, but luckily you'll always blindly choose to cut the right wire.
14. A detective can only solve a case once he has been suspended from duty.
15. Police departments give their officers personality tests to make sure they are deliberately assigned a partner who is their total opposite.