That is exactly the wrong use for a take 20. Taking 20 means accepting also getting a 1 on the way to getting to 20. If this conversation is meaningful enough to require a skill roll, then trying every possible avenue of conversation means you will surely imply something insulting about the target, his mother, his god or his fashion sense... thus preventing ever getting to that 20. There is a consequence for failure, so no take 20 allowed.
A take 10 might be fine, though, if he's a nice guy who is not averse to talking with strangers. Whether that 10 will be enough depends on the DC and your skills.