1. A person who is haughty is not accepted by others.
2. A person should not wear clothes suitable for a Torah scholar if he is not a Torah scholar.
3. A person who is hired to build a "bridegroom house" must build a house that is at least four by six Amos.
4. A son-in-law should not live in his mother-in-law's house.
5. It is inappropriate for a guest to invite another guest to the house of his host.
A BIT MORE
1. He is not even accepted by the people of his household, and his wife will end up denigrating him (Rashbam).
2. Hashem does not allow such a person to be close to Him.
3. This is the opinion of Rebbi Akiva. Rebbi Yishmael maintains that this is not sufficient, as this is the minimum size of a barn. (He does not say exactly how large the house must be.)
4. This is because a mother-in-law is suspected of being overly friendly with her son-in-law, especially her first son-in-law (as stated in Pesachim 113a), which may lead to illicit relations.
5. It is also inappropriate for a person to answer a question before he has heard the entire question.