Can my friend apply for the visa in Bangkok on my behalf? If i give them my passport and filled out form and photo

Yes, your friend can apply for the visa in Bangkok on my behalf if you give them your passport and filled out form and photo. Maybe the round-trip flight tickets and hotel booking are also required. However, you should still stay in Thailand, if the passport with the exit record of Thailand and the entry record of Uk/another country which shows you have left Thailand, you can't do it because it is illegal to mail the passport internationally.