Might Misuse.
I hear this a lot, particularly on the likes of Tipping Point: "I might go for drop zone 4".
I really hope I am not guilty of this one. I have a friend who does this all the time, replacing the definite "will" with the indefinite "might". When I am feeling particularly curmudgeonly (which isn't all that rare), I reply "when will you make your mind up?".
Then there's Rod Stewart on his Great American Songbook series of CDs. Lousy voice, but great music (and Louis Armstrong didn't exactly have a great voice either). For some inexplicable reason, in I've Got You Under My Skin (Cole Porter), in the line "I'd sacrifice anything come what might", Stewart substitutes "may" – apparently without any recognition "may" is grammatically incorrect, but most importantly that it doesn't rhyme with "night" two lines later! It's an insult to Porter, and grates on me every time I hear it (which is a pity, because otherwise the music is good).
Might: possibility
May: permission
Can: ability
"Only food bought here can be eaten here" – that's incorrect, and I can prove it (by eating my own sandwich, albeit without permission).