Add your own below, or fiercely contest mine.
1. If you're not driving, always have another drink.
2. If it's important, they'll call back.
3. Don't get on a two-wheeled vehicle unless you are content to die that day.
4. Don't eat anywhere where they have photos of the food.
5. Don't walk slowly on concrete (asphalt depends on context).
6. Be patient.
7. Always have another door to walk through.
8. Don't complain if you wouldn't like to be doing their job.
9. The customer is not always right.
10. Don't rely on anyone who wasn't present at your birth and isn't married to you.
11. Get over yourself.
12. If someone's buying you lunch, always order from the cheaper half of the options, even if they insist otherwise.
13. Assume nothing.
14. Seating arrangements are absolutely crucial, sometimes even life-defining.
15. Avoid the company of people who are keen on emphasising where they went to school.
16. Never go back and visit your old school. It diminishes the memories.
17. Never go to a school reunion.
18. Never use the Central Line unless you absolutely have to.
19. Visit everywhere once (but don't violate 62 in doing so).
20. Get someone's name spot on first time, especially if it's long and difficult.
21. Anything that makes the national news headlines is a lot bigger than you, so don't worry about it.
22. There has never, in the history of humankind, been an excuse to jump a queue.
23. Don't be a cheapskate.
24. Always talk to the least important person in the room.
25. Listen more than you talk.
26. Never skip the opening titles.
27. Never talk about money.
28. Attack in the morning, defend in the afternoon.
29. A vivid memory is better than a video.
30. The word 'hub' means that someone is trying to cut costs and lie to you about it.
31. Always vote in any election in which are you eligible to vote.
32. Speed of putting is more important than line.
33. Always call tails.
34. For anything with bays or aisles (toilets, parking spaces, cinema seats) always go as far away as possible from all other users.
35. Confirmation bias is the greatest threat to the discourse. Exhibit A: Jeremy Clarkson's A levels.
36. There is no shame in knowledge of any kind.
37. It's impossible to have more than ten friends.
38. There's nothing wrong with being afraid.
39. Don't wear a baseball cap after your 25th birthday.
40. Always point out the wardrobe malfunctions of others.
41. People who disapprove of sport are worthless.
42. Never sit in the front row.
43. Always have lunch with others, if you can.
44. If you play a game, play it properly.
45. Read everything, all the time.
46. All music is real music.
47. If your mother would disapprove, and you're not breaking the law, it's probably a good idea.
48. A locked toilet cubicle is the best place to deal with anxiety attacks in public.
49. Microsoft Excel can do literally anything.
50. The referee didn't cause you to lose.
51. People are the same everywhere, it's culture that differs.
52. Things fall apart.
53. Know the word for 'thank you' in every language.
54. Only get on a bus if you have exhausted all other options.
55. It's better to be a quiet drunk than a loud one.
56. Don't use cream in cooking.
57. Always listen to people younger than you. Even if they're wrong, they'll soon be right.
58. Don't joke about someone's name. They've heard it many, many times before.
59. Spend money according to how many minutes you use things for. Bedding, chairs and shoes should be premium end.
60. Avoid people who complain about the price of things.
61. The good old days were actually terrible.
62. Do not visit countries where you are illegal.
63. Feeling comfortable > looking good, though both are handy.
64. Runs on the board in a final.
65. It's not sad to do things on your own.
66. Don't compare your problems to those of others. The fact that children starve doesn't mean you can't feel sad about the lack of aioli in Waitrose.
67. Never do anything involving the use of an oxygen tank.
68. Wear sunglasses as often as you can. They are a licence to glance.
69. Reversion to the mean is unstoppable, so don't try.
70. Don't rely on other results going your way.
71. Don't be ashamed of your upbringing. You had no choice in it.
72. If everyone is happy, no one is happy.
73. When outside the British Isles, just accept that breakfast will be shit.
74. Don't talk about politics with people you like.
75. Buy new socks regularly.
76. Don't aim for perfection. Aim for really good.
77. Never invite yourself to anything.
78. Always know the law inside out.
79. You don't look good in lycra.
80. White men can't play spin.
81. Always have money on you.
82. It really helps to be excellent at geography.
83. Don't kill insects, apart from mosquitos.
84. Take your medicine.
85. The team that needs to win usually does.
86. Always follow dress codes yourself, but don't judge others for not doing so.
87. Never go off-menu and never ask for an item to be removed from a dish.
88. Don't cancel a social engagement unless it's an emergency.
89. Pronounce foreign names correctly, but in your own accent.
90. Always offer to wash up.
91. Don't trust anyone with noticeably excellent social skills.
92. Don't think you can understand other people's families.
93. Never write off the Germans.
94. Plan your potential escape from any room.
95. Always take account of the weather forecast.
96. Don't use brute force.
97. If in doubt, kiss them.
98. If in doubt, it's always a scam.
99. If in doubt, say yes.
100. If in doubt, shut the fuck up.