Tarek El Moussa Allegedly Goes Off on Ex, Christina, on 'Flip or Flop' Set

Tarek El Moussa flipped out on his "Flip or Flop" costar and ex-wife, Christina Haack, for letting him know it was time to film ... sources close to the show tell TMZ.

According to our production sources ... Tarek's eruption went down on the set of the popular HGTV series last Wednesday, after he apparently didn't like the way she signaled to him that she and the crew were ready to begin shooting.

We're told Tarek immediately lost his cool and went on a verbal tirade directed toward Christina ... which allegedly included him comparing her to his fiancee, Heather Rae Young, and saying Heather is hotter and richer than Christina.

Our sources say Tarek boasted that he "made" Christina and called her a "washed-up loser," and exclaimed that he enjoys watching her fail.

We're told he also yelled "Look at me, look at me, look at me. It’s called winning" and capped off his rant by screaming at her ... "The world knows you're crazy!"

According to our sources ... this isn't the first time Tarek went on a tirade against Christina on set. We're told after the latest incident, production stopped filming them together for the rest of the day ... and simply shot their scenes separately.

A source close to Tarek tells us his anger toward Christina stems from her recent admission she smoked toad venom -- before meeting her new boyfriend -- and his main concern is for the safety of their two children. At the end of the day, both Tarek and Christina are show execs, and our source says there's going to be tension from time to time, this was one of those incidents.

We reached out to reps for Tarek, Christina and HGTV ... so far, no word back.

As you may know ... Christina's made headlines as of late for following up her divorce from Ant Anstead by revealing she's in a new relationship with Joshua Hall -- something that came about after she says she smoked toad venom.