Is a Sarcastic Hand Gesture Possible?

I managed to keep a Porsche behind my for about half a mile (...)

It's not really nice, is it? I hope he was a dick before you did it.
If not, it's just silly.
There are many adults on this forum who also drive cars - they are courteous towards fellow cyclist and expect the same in return and not deliberate obstruction :-P

I usually give a thumbs up to thank drivers when they do good things like using their common sense & giving me way when there is space for ONE to get by, however, Friday on Broadway market I did this and as I passed the driver of the van that gave me way was like,

WHAT?!?

So I u-turned to explain what he might have been thinking was wrong. He thought I gave him the middle finger so I apologised and said 'non'. We're friends now, he had a lot of people giving him shit that day. The point is I now wonder how many drivers have mis-interpreted my thumbs up as needless rude/aggressive behaviour?

It's all in the eye contact I guess?

Waving is less likely to be interpreted as flipping the bird.

Unless perhaps you're waving your cock at them..