(An oldie but a goodie
Beware of synthetic oil; it can do terrible things to you and your beloved motorcycle. It will not only leak out of your engine faster than you can put it in, but it will also cause your oil filter to clog and implode, dumping debris and dirt into your lubrication system.
It also will make every part of your bike permanently slippery because of its linear molecular chain dispersion action. Then it will leak onto your kickstand causing it to retract automatically, dropping your bike on the ground! But that's not all...
Synthetic oil will round off your gears and spin your bearings. It will Also splatter onto your seat causing your girlfriend to fall off in the apex of a turn and she'll never ride with you again.
Synthetic oil coats Your sight window and your timing window with a whitish pro-emulsification additive that is both non-removable and highly corrosive. Synthetic oil will completely leak onto the ground overnight and your dog will drink it and die. Synthetic oil will wear out your tires and make your battery leak. It will give you the desperate need to urinate after you put your full leathers on and then jam your zippers shut.
It will contaminate your gasoline causing your bike to stall on railroad tracks and accelerate uncontrollably near police cars. It will make it rain during rallies and on weekends. It will lubricate your timing belts causing them to jump teeth and break your valves to bits. Synthetic oil chemically weakens desmodromic valves and causes the clearances to change every six miles. Then it melts the black soles of your riding boots night before you walk across your new carpeting.
While riding past groups of attractive women it will cause both of your handlebar grips to slip off at the same time so you smash your windscreen with the bridge of your nose. It also causes your swingarm to crack, your studs to break, and your rotors to warp, and then it voids your warranty by changing your odometer reading to 55,555. It also dries out your wetclutch and wets your dryclutch. It makes your clutch slave cylinder seal fail in the heaviest traffic on the hottest day of the year while putting an angry wasp in your helmet for good measure.
Synthetic oil hides your 10mm socket and puts superglue on your earplugs. Synthetic oil will scratch your faceshield and make your gloves shrink two sizes night before trackday. Synthetic oil stole your neutral and sold it to the Chinese for $1.25.
Synthetic oil will make you grow a tail. Synthetic oil will write long crazy e-mails to your Internet friends and then sign your name at the bottom.