Friendships between NBA stars from different teams are far more common today than they were a generation ago. Does the same apply to NBA coaches?

Not for Joe Mazzulla.

The Boston Celtics head coach explained Friday that he’s cordial with and respectful of his counterparts from other clubs. He’ll occasionally reach out to some and always is looking for lessons he can draw from other coaches’ styles.

Get too close, though, and you might inadvertently give away a competitive advantage, which Mazzulla is dead set on avoiding.

“There’s a cordiality there, but it’s very important not to give away psychological tells — things that can lead to an opportunity to give away a psychological leak,” Mazzulla said. “So I just try to be cordial without giving away those psychological components.”

That even applies to coaches Mazzulla knows well. Take Charles Lee, for example, who spent one season as Mazzulla’s top Celtics assistant before leaving to become head coach of the Charlotte Hornets.

“I told Charles when he left, ‘I’m not talking to you during the season. I’m not waving to you at the national anthem. I’m not doing that. You’re an enemy,’” Mazzulla said.

Before Boston and Charlotte met earlier this season, Mazzulla said Lee “breached NBA rules and came into the assistant coach locker room and forced me to give him a hug.”

“That could easily be a psychological tell that knocks you off your game competitively,” he said. “So he knew what he was doing.”

Was it at least nice to hug Lee, with whom Mazzulla won an NBA championship this past summer?

“No,” Mazzulla replied, straight-faced.