This is where a persons, eyes begin to spin around and look in different directions. This usually occours when the person is drunk and/or on pills/ drugs (hence the smack reference)
It then can be used as an effectionate nickname for the said person.
It is named after the legend that is "Smack Eyes, some claim that he was found and raised by a family of crack fiends others say he was born, when a rogue heroin dealers drug factory exploded and a monkey got effected by the fumes and raped a passing Nun. This man then walked the streets and terrorised people and did crazy things like kick dogs and pulled fire alarms.
Yo Bro, Liam is crazy bro, this one time he was on pills and he kicked a dog and pulled a fire alarm, he had proper Smack Eyes Bro