In this case, I think MM already knew Clark's full name and much more than that, but in general I think Clark might be wise to not offer the bad guys his name so easily.
To be fair, MM had already addressed him as "Mr. Peters", and given that Clark got picked up from his own home, MM could have found out his full name from a quick glance at almost any mail that might have been lying around - I think Clark's a little bit beyond worrying about whether MM knows his name...
As for Machismo knowing Clark's name, he admitted as much to his inmate buddies back in Strip 101 (http://dudeindistress.thecomicseries.com/comics/130/#content-start). Of course, Clark isn't aware of any of this, but since the guy was waiting for him in his apartment, he probably figures his identity is the least of his worries at the moment.
Since it has been shown that MM has been watching Fem the whole time, I suspect he knows a lot more then what has been mentioned here. And I imagine that this is why a certain super heroine has not had more boy friends. Anyone that seemed to catch her attention did not stay around for long. At least not amongst the living.
If Machismo actually murdered or scared off her other suitors, I'd imagine she would have already figured that out. Note Machismo didn't intervene until Clark managed to make it to date #3, which nobody on Earth had managed up until this point. I'd say all the others fell through without Machismo's interference.
