1 Corinthians 14:23
If therefore the whole church be come together into one place, and all speak with tongues, and there come in those that are unlearned, or unbelievers, will they not say that ye are mad?
Cross-reference
In 1 Corinthians 14:16, Paul explains that the unlearned cannot say Amen to a blessing they don't understand — directly reinforcing the problem of confusion from tongues.
In 1 Corinthians 12:10, tongues and interpretation are listed as gifts — providing background for why uninterpreted tongues cause confusion in worship.
In 1 Corinthians 11:17, Paul criticizes the church for coming together for the worse — both passages address disorder in corporate worship that harms the assembly.
In 1 Corinthians 11:18, Paul also addresses problems when the church assembles — here it's tongues causing confusion, there it's divisions.
John 10:20 records people saying Jesus is 'raving mad' — the same accusation of madness appears here against tongues-speakers.
Acts 2:13 shows the same reaction to tongues — onlookers mocked Pentecost as drunkenness, just as here they call tongues 'out of mind'.