How to unplug this connector? Tried everything that came to mind.

 It has a latch on one side, all attempts were done while pressing it down fully.

Connector was cleaned all around, then heated up a bit (warm to touch) using a hairdrier. It won't move no matter how hard I pull it side to side etc. I tried to insert a very small screwdriver on the long sides to push downwards but still no go. Tried to grab it with small pliers, won't move.
 The connector has a very tight fit, so if I try to spray WD40 inside it will make a mess and nothing else.

 Any ideas? The photo is taken before cleaning it up etc. 

Not sure but I thought the lug on the bottom right of your photo had to be pushed in towards the connector and then plug would pull apart. Usually pretty tight though.

Push in the direction of my poorly draw arrow while pulling the connector apart I think. 

You must clean off all that muck and that includes the recess where the latch sits. DO NOT PULL THE PLUG BY THE WIRES. To do so will likely damage the connectors. When thoroughly clean wobble the plug and the socket to break the bond. A good spray with WD40 will usually help. The clip usually will need pushing in. Have a good look at it, if necessary use a good light and a magnifying glass. If the clip wont move, there is still muck jamming it. I would suggest a smear of vaseline on the pins and sockets, but they must be clean before you do so.

Roger

wrote:

 It has a latch on one side, all attempts were done while pressing it down fully.
 

 Thanks guys, but as I said in the OP this isn't a problem of not pressing down the latch/lug situated on the side of the connector. All the attempts were done while pressing it down fully.

Was hoping there may be some clever way to pull it out without breaking it.

Looking at it I would say that the small red part is potentially some kind of interlocking device that needs to be lifted out of the connector first, it's probably captive and has an open and close position. Do you know what circuit it is on/location on the car?