This list is a compilation of mostly random, detrimental effects, problems, and conditions that can affect a character. DMs should pick results that correlate with the actions or events that lead to a Bad Thing having to come into play. The severity of these varies, and some are suitable as player flaws, although that is not the main focus of the list.
1: Your hair and nails grow uncontrollably fast.
2: You grow bald.
3: You attract flies and other vermin.
4: Snakes follow you around.
5: You no longer appear in mirrors. (Great in worlds where this is a sure sign of vampirism ;) )
6: Your touch rusts metal
7: Your skin turns to a non-natural color, permanently.
8: You fall under a magical laughing spell whenever it's socially unacceptable to laugh. (Funerals, audiences with the king, moments of silence, religious ceremonies...)
9: Animals flee your presence in terror.
10: It is always horrible weather around you.
11: Any ship you step on doesn't arrive at its destination due to storm, mutiny, or other bad happenings.
12: Your presence causes waves to double in height.
13: Others around you cannot fall asleep.
14: Your touch causes water to become stagnant and bitter.
15: All food loses taste.
16: Your body waste ignites spontaneously with air.
17: Fires cannot be put out in your presence.
18: Your skin turns transparent.
19: Potions have the the opposite of intended effect on you.
20: Kobolds believe you are their God trapped in flesh form, and believe the only way to release that God is to kill you.
21: You are cursed to fall down flights of stairs, without fail.
22: You cannot enter a town without being robbed or pickpocketed at least once.
23: Cats horde around you, meowing as if you had catnip in your pocket.
24: You become allergic to beer.
25: Anything you cut with a bladed edge starts screaming as if it were alive.
26: Your hands shake uncontrollably during fine tasks.
27: Your presence makes fires randomly explode.
28: Horses refuse to listen to your requests.
29: Squirrels, skunks, weasels and other woods animals invade any home you sleep in.
30: A bear believes you are its mate and refuses you to have contact with any other living creature.
31: You fall twice as fast as a normal person.
Additional Ideas (4)
33. You say out loud what others think, all the time.
34. Within 10 yards of you, milk curls, wine goes sour and food spoils.
35. Ghastly voices speak from your ears in tiny voices, demanding things.
36. You glow with an eerie light.
37. Your hair stands automatically every time you spot an officer of the law.
38. You sneak into strangers houses on busy evenings against your will.
39. When you speak to people they automatically say what you intended to say and the other way around.
40. A cool and unnatural wind blows from your mouth every time you open it.
41. A majestic crown of shimmering fire floats above your head.
42. You appear to be exactly where you are, but in a different and random activity.
61. You can only tell the truth.
62. Any water you touch becomes bitterly cold. Good for ice-cold drinks, but say goodbye to hot showers. Rain sucks, too.
63. You have an annoying song stuck in your head for all eternity, causing distraction and possibly insanity.
64. You hear all of your actions narrated by a disembodied voice with a dry sense of humor.
65. You can't enter a forest without being tripped by tree roots, hit on the head by falling branches, or possibly crushed by a wayward tree.
66. You cannot cook without a catastrophic failure.
67. Squirrels attack you on sight.
68. Your right hand swells to two times normal size, permanently.
69. Passing vehicles always splash you in wet weather.
70. Those you find repulsive find you absolutely beautiful.
71. Magic proclaims that you do not exist.
72. You can no longer hear music. (Quite possibly the most horrible curse that could exist on this list.)
73. Your body does not form calluses.
75. Lightning strikes dwellings you sleep in.
76. Sources of illumination giggle madly in your presence.
78. You can only eat and derive nourishment from raw pine cones. Every thing else cause "bodily regection."
79. You have constant allergy/sinus problems for the rest of your life.
80. An town crier that no one else can see or hear constantly announces your business both public and private.
81. Same as 80, but everyone can see and hear him.