Have You Ever?

Nope

Have you ever fucked someone's gf/bf behind their back?
 
Yes

have you ever caught you mother doing sex with an other man
 
Fortunately no. Multiple women have occasionally been enthusiastic enough that I popped out while they were bouncing on top of me, but damage done, slid right back in and continued with the fun.

Have you ever has someone so hungry for your cock that they unzipped your pants and sucked off right after walking through your door?
 
Not full-blown sex, but I jacked off a guy sitting next to me on an overnight flight from Europe once. (Under a blanket of course, and in a two-seat row. We stayed in touch a bit afterward. He's well known enough to have a Wikipedia page but not famous.) I think it was to orgasm, so it probably counts.

Have you ever been to South America?