You keep it business professional. 3? 4? years down the line - you run into him / her and they've changed (in whatever way) - maybe you have to work together a

You keep it business professional. 3? 4? years down the line - you run into him / her and they've changed (in whatever way) - maybe you have to work together again or choose to work together again. Ie: never burn a bridge. Unless they killed your cat or dog or sued you - it's not worth it.