Ive been best man once before and the line i used worked pretty well.

I basically started the usual good evening ladies and gentleman. Then went on to say how odd that history repeats itself. 23 years ago chloe was going to bed with a dummy and here we are again all these years later. (await the titter cos i got a good response from that opener) then apologise to the groom "sorry mate...but as best man it is my duty to give you the most uncomfortable 5 minutes of your life...consequently ladies and gentleman the most uncomfortable 5 minutes of chloes life will come later tonight courtesy of Sam"

You might want to chuck in a couple of gags about cacking yourself. I thanked the chef for the lovely meal then said my share should be hitting the southampton cetral sewer right about...now.

Shitty jokes mate but its not a comedy club. people want you to do well. Also remember they will be well oiled with a bellyful of grub. Enjoy the day and dont have too much to drink before your speech

have also been to riga on a stag do so if you want any tips