In [722]: df[(df['C']==1) | df['B']]
Out[722]:
   A      B  C
0  1   True  1
2  2  False  1
3  2   True  2
4  3   True  1

In [723]: df.query('C==1 or B==True')
Out[723]:
   A      B  C
0  1   True  1
2  2  False  1
3  2   True  2
4  3   True  1

In [724]: df[df.eval('C==1 or B==True')]
Out[724]:
   A      B  C
0  1   True  1
2  2  False  1
3  2   True  2
4  3   True  1