Tristan Thompson appears to have beef with Lamar Odom ... and Khloe Kardashian is smack in the middle of things.
Here's the deal ... Khloe posted an Instagram photo Friday showing her taking an outdoor shower in a skimpy bikini, and Lamar complimented her in the comments, telling her she's a "hottie" ... a response Tristan's not taking kindly.
Tristan tagged Lamar in the comments and then seemed to loft a threat his way, writing .