There was a time, say 1987, when it was thought the height of sophisticated proto-hipster humor to shout "Freebird!" at a Galaxie 500 concert. It was funny, see, because it was the exact opposite of what everybody wanted to hear.
If it was ever amusing, it no longer is. Nor has it been for some decades now. So unless you're attending a Lynyrd Skynyrd concert (minus the three band members who tragically died in a 1977 plane crash), just please don't yell "Freebird" at any concert. Period.
When making real song requests, try pitching one the musicians are actually known to have written and/or recorded. They'll be that much more likely to perform it for you. Ideally it should be a slightly obscure tune from an early album. Your request will simultaneously flatter the performers that they have dedicated fans, while introducing new fans to something they might not have heard.
In any case, try saving your song-suggesting shouting for times the band actually asks for it.