If you are flying in a threat rich enviornment at a high enough altitude that you can be tracked and locked with an IR or radar missile, you deserve to get shot down.
You will get a warning when someone locks you up with a radar guided missile (due to you being lit up with the radar waves RWR).
IR is a passive sensor (it only reads what you give off) that will not warn you.
don't fly like this guy, high helos make for an easy target.
(about video): when he pulls the rod, liquid nitrogen is cooling the warhead so that it can get a good lock, the guy holding the camera was counting to 10.
The way to avoid getting shot down by manpads etc. is to fly as low as you can and use the terrain to mask yourself.
By flying low and using trees etc. you won't be visible long enough for someone to get a lock.
IRL flares are the equivalent to cross walk buttons, (they just make you feel better) they have been made obsolete by the advanced IR/UV seekers in today's missiles. missiles today don't lock on to the "hottest" target, when you lock they remember the specific heat heat cross section that you locked on to, throwing out flares that even match temperature won't match the size of the object that was locked and the missile will ignore them. They also don't need to "hit" they just need to get within a set range, and depending on the type of missile will direct the "explosion" or "expanding - rod" into the target.
I will say that the time to equip, lock, and fire an AA missile is much too short.
TLDR; don't be bad fly low, if they lock and fire on you, you let them do it.