While grabbing his morning cup of java at Coffee Bean in West LA, Ashton Kutcher chooses his words wisely when asked about whether or not he actually cheated on wife Demi Moore.

Kutcher remains tight-lipped ... however as he slips into his black Lexus, Demi's hubby couldn't resist telling our X17 videographer, "You know better."

Earlier this week, Kutcher's lawyer, Marty Singer, described Star Magazine's cheating allegations as "lies" and "reckless conduct."

Demi and Ashton have been married for five years.