You become who you hang out with

"Do not be deceived: `Bad company corrupts good morals.'" (1Cor15:33 NASV)

deceived = πλανάω = seduced. to wander away.
corrupts = φθείρω = withers or shrivels. to spoil (as in food)

the CEV puts it this way:

"Don't fool yourselves. Bad friends will destroy you".

Paul was an intellectual and can be seen here quoting a common phrase of the day from Menander (a Greek dramatist) who in turn had quoted it in one of Euripides' earlier plays. The Jamieson-Fausset-Brown Commentary tells us the meaning from the play indicates communion with "those who deny the resurrection". The Church at Corinth had fallen back into a sinful state since Paul had left them. And Paul puts some emphasis on the company they keep for this slippage. Your morality is strongly influenced by the company you keep. Those who deny the resurrection are bad company for close friendships.