Best speech I've seen was the best man rigging up a 'lie detector'. He then proceeded to ask the groom a few testers to check the system was calibrated:

'Have you ever wondered what you'd look like in tights'?

'NO!'

System buzzed and the red light flashed

'Well, now I know it's working properly...'

He then proceeded to work his way round the room stitching up the groom and his mates