Some funny quotes a best man can use include this one from George Bernard Shaw: "It is a woman’s business to get married as soon as possible, and a man’s to keep unmarried as long as he can." A George Nathan quote is, "Marriage is based on the theory that when a man discovers a particular brand of beer exactly to his taste, he should at once throw in his job and go to work in the brewery."
Many funny quotes that a best man can use are not attributed to any one author, but rather have been handed down over the years, such as, "It’s been an emotional day. Even the cake is in tiers."
Often the best man joshes the groom in his speech, but may also make fun of himself, especially about how nervous he is giving a speech. He can do both, as in the line, "If there is anyone here who is feeling worried, nervous or apprehensive, you're either me or you just married the groom."
Some quotes may be a bit risqué, so before using them, a best man may want to ensure no one at the reception is likely to take offense. It is usually best to avoid off-color jokes or ones that could be misinterpreted.