let the fun begin
Crazy Taxi Driver - hire a taxi and select a location on the other side of town, once the taxi starts moving tell the driver to "hurry up" and he will start driving recklessly crashing into things and ignoring stop signs and red lights. Then increase your wanted level to maximum, and enjoy the ride. Its hilarious to watch the cops slamming into you and shooting at the driver from the safety of the back seat

Mad Playground - Theres a swing set in a playground in south slopes that has a glitch in it, drive a car up to it, hit it, then park up touching it and it will send you flying, dam insane, from ryan

Stunt - complete all the bike stunts around the city there is around 50 from what I remember.

Fire Hydrant- Blow the top off a fire hydrant then jump on your bike and ride that wave sky high:)

911 - Call the cops and then rush around punching as many people as you can when the cops arrive they will see people attacking you and promptly arrested those mean mean people. You can also call the fire brigade and ambulance.

Fire Department - jump in a firetruck and give those dirty homeless a good spraying.

Car Domino's - Line up a whole bunch of cars then fire off a rocket or grenade to see a domino explosion effect, you may have to make sure you've damaged the cars enough.

Army Chopper - Visit the airport and grab the army helicopter with the minigun and terrorize the island.

Airport Madness - Get a full wanted rating and then head to the airport with a bike and run circles around the cops its especially fun to place yourself in the middle of the back wheels of a moving airplane and watch the cops try to get to you cause nothing stops a giant boeing 747 , those cops get squished and thrown around all over the place.

Friendly Fire - play a lan game with friendly fire off and hit each other with those rockets and watch yourself fly like a birdie.

Stripathon 3some - go the strip club and get as many lap dancers into the private room as possible ( this can get quite tricky to get the dancers to ask you for a private dance but ppl have been known to get 2 or even up to 3 dancers into one room)

Cinematic Challenge - grab a fast car or a strong vehicle switch on cinematic camera mode and see how long you can last while the cops are after you it can be quite entertaining in this camera mode.

Pool throw - start a pool game then get out and just pelt those balls at your opponents head , no one messes with nico bellic

Scream Wheel - grab a car that's full of passengers and take them for the ride of there life , you wont even need the radio on cause they provide enough noise through screaming and oh my god'ss.

Really Rough S*XX - Go find your local hooker and get her into your car, then use your mad driving skills to get the car to flip over and then do the dirty business upside down.

Burnouts - hold the forward and backwards keys at the same time and see that smoke go ( not much smoke really) but you can do donuts by using the directional keys which is quite fun.

Bike simulator - grab a bike, then switch into first person view and try and drive at high speeds without crashing ( can be quite tricky).

Fastest Car - Near the old mansion on alderny island , you will find one of the fastest cars in the game the Sultan RS

Falling Boat - use the boat cheat code to drop a speed boat on unsuspecting people. I may add a gta 4 cheats page if there isn't already one

No hands - grab your sniper rifle or any other gun if your accurate and shoot the driver of a car straight in the head, sometimes he will come to a stop other times he will keep driving all over the place fun to watch.

Fast lane - grab a bike and find the longest road you can find then fly down it without crashing.

Drunken Bowling - go get drunk at he bar then hit the bowling centre its tricky stuff that 10 pwin boolin.

Down with the Burgers - head towards a burger place or cluckin bell grab a car and barricade the door jump over the car into the restaurant and cause havoc and see how long you can withstand the cops, as long as the car blocking the door stays in tack it could last forever but it usually gets blown up eventually.

Look Ma no tires - blow up all the tires on your car jump in , get a wanted level and see how long you last.

Choppy - use the chopper blades to rip people to bits.

Watch me die - ofcourse another great fun part of GTA 4 is the video editor which you can use to create some pretty funny dying sequences and add music , effects and all that other swish stuff.

Hit that boat - find a ramp near the water and drive your bike off it and try and hit a boat thats driving by. extremely tricky to do:P

Rollercoaster Fun - Head over to the fun park on Firefly island grab a nice smallish fast car and wizz around the roller coaster track.

Pig Ride - Grab a helicopter and get a decent wanted level , land your helicopter and try and take off as the cops try and drag you out , now fly off with the cops clinging onto your chopper, and belt them around the skyscrapers.

Hooker Free or Not - Go pick up an old fashioned hooker off the streets in your car, find somewhere quiet to park your car and send the kids out of the room, then you can choose whether or not to let her keep the money you just paid her.

Carpark Frenzy - Get a high wanted level and then head to a crowded car park and wait for the explosion. I hear there's a crowded car park in alderney island

Fly a Friend - Great fun on multiplayer is to jump in a helicopter with a friend then try and drop him off on unreachable buildings, or even drop him on the top of the statue of liberty.

Move Aside - I'm sure you probably have tried it but get a cop car or fire truck and put the sirens on and everyone will clear a path for you on the road.

Probably the most fun you can have it playing the multiplayer with a bunch of friends so lots of stuff to try out there also the GTA 4 engine and physics are quite well done so testing all the physics out can be great fun.