The best part about Mystique was not how obvious it was she was flirting when she threatened to kill him, although  the implied mixture of sex and violence when she threatened to do something like rip his heart out and throw it in a garbage disposal really got Sabretooth going. 

No, the best part was she was into the same thing. He could smell the attraction on her when told her just how far he’d like to get his claws inside of her. Hear the hitch in her breath and her heart race. What a bloody tango pair they made.