As prem dai suggested if you do not want to get out of airport you do not need transit visa..... given the tight flight schedule you have and traffic problem in bkk I do not think getting out in bkk and getting laid is great idea.. ;-) but if you are considering hkg too then you need transit visa.. hkg doesnot allow nepalese to get off the plane unless you have transit visa.. I remember on feb when i was comming back from nepal to US, I did not have transit visa, as soon as plane landed and I came out of RNAC flight there were hkg cops in 100s checking each and every ones passport, they did grill me for 15mins before letting me go to the transit lounge.. But recently they changed the rule and said they wont let nepalese step into their land unless they have some kind of visa ....