Default guest avatar + Hover Effect

.dfavatar-box {
    border-radius: 50%;
    overflow: hidden;
    margin-top: -22px;
    margin-right: 15px;
    background: #fff url('images/default_avatar.png') no-repeat;
    background-size: 100% auto;
    float: left;
    width: 35px;
    height: 35px;
    border: 6px solid #111;
}

.dfavatar-box:hover {
    -moz-transition: all .5s ease-in-out;
    -webkit-transition: all .5s ease-in-out;
    -o-transition: all .5s ease-in-out;
    -ms-transition: all .5s ease-in-out;
    transition: all .5s ease-in-out;
    -moz-transform: rotate(720deg);
    -webkit-transform: rotate(720deg);
    -o-transform: rotate(720deg);
    -ms-transform: rotate(720deg);
    transform: rotate(720deg)
}

<div class="dfavatar-box"></div>