I think it really depends on how you wish to spend your night life teeth_smile ex on Kao San road you can find many tourists there spending their night time in pubs, walking around that street, shopping, dining, sitting and watching the people spending nightlife etc.

If you are looking for exciting nightlife you can go to Patpong, Silom, Soi Cowboy there are some shows and pubs that you might not want to miss heheshocked.

On the other hand youu can also enjoy your dinner along the river on the boat regular_smile, being on Tuk tuk for sight seeing at night is also good idea wink_smile

Enjoy then!