If you're flying in the closest airport is in Koh Samui (USM). You can buy a taxi/ferry ticket combo to Koh Phangan in the departure lounge.
The Haad Rin Queen ferry leaves from the Big Buddha pier at 10.30, 13.00, 16.00, 18.30 and takes approximately 50mins.
From Haad Rin pier it's just a 5 minute walk.
Continue straight down the main road past the 711 until you reach an intersection (known locally as Chicken Corner).
Turn right, carry on 50m, just after you see Sand Castle Bar take the next left towards the beach.
Fubar is on the right side of the road half way down.
From Thong Sala pier ask the taxi driver to go to Haad Rin.
Ask to be dropped at Fubar (Tonson Road).
If for any reason they drop you anywhere else in Haad Rin don't panic as it's a very small town so ask around for 'Chicken Corner' and follow the directions above!