I got Practically Canadian, Thorn in Side, and Hometown Hero in one match.
I got a little lucky since MP is somewhat barren and in my ranked CTF match (and it needs to be ranked to get all 3) it was just me vs. one other player. So wait for a ranked 1 on 1 CTF game on a map you know and just hide a bit around your flag until it is captured then spring out and get the kill and return. since it is just 1 on 1 you automatically can get the return if you get the kill.
For Pacifist i was certain i had it unlocked the first time i went for it. i had two flag captures and no kills or even firing of weapons...EXCEPT for the KNIFE. i used the knife to kill a raptor or few during the match and the achievement didn't unlock. so bare that in mind... don't attack/kill anything. I finally unlocked this one in a similar manner to get above achievements: another 1 on 1 CTF map. lucky again in that my competition didn't seem to know the map as i captured the flag 3 times really quick without seeing the guy at all.
it's fairly common, for me atleast, to get into 1 on 1 games even when searching for large team games.